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This Guide Is Primarily About TCP/IP Network Protocols And Ethernet Network Architectures This Guide Is Written For All Audiences, Even Those With Little Or No Networking Experience.


A Network Is Any Interconnected Group Of People Or Things Capable Of Sharing Meaningful Information With One Another. Is A Collection Of Computers And Devices Interconnected By Communications Channels That Facilitate Communications And Allows Sharing Of Resources And Information.

Data Networks Are Important To All Contemporary Organizations Because They Provide Faster, Easier Access To Any Message Or Data That Can Be Represented And Stored In Digital Format. In Addition To Data Sharing, Computer Networks Also Enable Resource Sharing, An Important Consideration In All Budget-Conscious Organizations.

General Network Design Process Access Needs And Costs Model Network Workload Select Topologies And Technologies To Satisfy Needs Simulate Behavior Under Expected Load Perform Sensitivity Test Rework Design As Needed

  • A Network Can Be Defined As A Group Of Computers And Other Devices Connected In Some Ways So As To Be Able To Exchange Data.
  • Each Of The Devices On The Network Can Be Thought Of As A Node; Each Node Has A Unique Address.
  • Addresses Are Numeric Quantities That Are Easy For Computers To Work With, But Not For Humans To Remember.
  • Some Networks Also Provide Names That Humans Can More Easily Remember Than Numbers.


    Network Operating Systems (NOS) Typically Are Used To Run Computers That Act As Servers. They Provide The Capabilities Required For Network Operation. Network Operating Systems Are Also Designed For Client Computers And Provide Functions So The Distinction Between Network Operating Systems And Stand Alone Operating Systems Is Not Always Obvious.


  • File And Print Sharing.
  • Account Administration For Users.
  • Security.
  • Installed Components.
  • Client Functionality.
  • Server Functionality.


  • Account Administration for users.
  • Security.
  • File and print sharing.
  • Network services.
  • File Sharing.
  • Print sharing.
  • User administration.
  • Backing up data.


  • LAN - Local Area Network.
  • WLAN - Wireless Local Area Network .
  • WAN - Wide Area Network.
  • MAN - Metropolitan Area Network .
  • SAN - Storage Area Network, System Area Network, Server Area Network, Or Sometimes Small Area Network.
  • CAN - Campus Area Network, Controller Area Network, Or Sometimes Cluster Area Network.
  • PAN - Personal Area Network.
  • DAN - Desk Area Network.

    LAN And WAN Were The Original Categories Of Area Networks, While The Others Have Gradually Emerged Over Many Years Of Technology Evolution.

    Note: That These Network Types Are A Separate Concept From Network Topologies Such As Bus, Ring And Star.


  • LOCAL AREA NETWORK (LAN): Which Is Usually A Small Network Constrained To A Small Geographic Area. An Example Of A LAN Would Be A Computer Network Within A Building. In A Typical LAN Configuration, One Computer Is Designated As The File Server. It Stores All Of The Software That Controls The Network, As Well As The Software That Can Be Shared By The Computers Attached To The Network. Computers Connected To The File Server Are Called Workstations. On Most Lans, Cables Are Used To Connect The Network Interface Cards In Each Computer.

  • METROPOLITAN AREA NETWORK (MAN): Which Is Used For Medium Size Area. Examples For A City Or A State. Networks Purpose Is To Share H/W And S/W Resources Among Its Users.

  • WIDE AREA NETWORK (WAN): That Is Usually A Larger Network That Covers A Large Geographic Area. Such As India, The United States, Or The World. Dedicated Transoceanic Cabling Or Satellite Uplinks May Be Used To Connect This Type Of Network. Connected Thru Public Networks Such As Telephone Lines, Leased Lines Or Satellites. Largest WAN Is Internet.

  • WIRELESS LANS AND WANS (WLAN & WWAN): Are The Wireless Equivalent Of The LAN And WAN.

    Networks May Be Classified According To A Wide Variety Of Characteristics Such As Topology, Connection Method And Scale.

    All Networks Are Interconnected To Allow Communication With A Variety Of Different Kinds Of Media, Including Twisted-Pair Copper Wire Cable, Coaxial Cable, Optical Fiber, Power Lines And Various Wireless Technologies.

    The Devices Can Be Separated By A Few Meters (E.G. Via Bluetooth) Or Nearly Unlimited Distances (E.G. Via The Interconnections Of The Internet). Networking, Routers, Routing Protocols, And Networking Over The Public Internet Have Their Specifications Defined In Documents Called RFCS.

    Before The Advent Of Computer Networks That Were Based Upon Some Type Of Telecommunications System, Human Users By Carrying Instructions Between Them performed Communication Between Calculation Machines And Early Computers. Many Of The Social Behaviors Seen In Today's Internet Were Demonstrably Present In The Nineteenth Century And Arguably In Even Earlier Networks Using Visual Signals.


    TCP/IP Includes A Wide Range Of Protocols That Are Used For A Variety Of Purposes On The Network. The Set Of Protocols That Are A Part Of TCP/IP Is Called The TCP/IP Protocol Stack Or The TCP/IP Suite Of Protocols.

    The TCP/IP Model Is A Description Framework For Computer Network Protocols Created In The 1970s By DARPA, An Agency Of The United States Department Of Defense. It Evolved From ARPANET, Which Was The World's First Wide Area Network And A Predecessor Of The Internet. The TCP/IP Model Is Sometimes Called The Internet Model Or The Dod Model.

    The TCP/IP Model, Or Internet Protocol Suite, Describes A Set Of General Design Guidelines And Implementations Of Specific Networking Protocols To Enable Computers To Communicate Over A Network.

    TCP/IP Provides End-To-End Connectivity Specifying How Data Should Be Formatted, Addressed, Transmitted, Routed And Received At The Destination. Protocols Exist For A Variety Of Different Types Of Communication Services Between Computers.

    TCP/IP Has Four Abstraction Layers As Defined In RFC 1122. This Layer Architecture Is Often Compared With The Seven-Layer OSI Reference Model; Using Terms Such As Internet Reference Model, Incorrectly, However, Because It Is Descriptive While The OSI Reference Model Was Intended To Be Prescriptive, Hence Being A Reference Model.

    TCP - TCP Breaks Data Into Manageable Packets And Tracks Information Such As Source And Destination Of Packets. It Is Able To Reroute Packets And Is Responsible For Guaranteed Delivery Of The Data.

    IP - This Is A Connectionless Protocol, Which Means That A Session Is Not Created Before Sending Data. IP Is Responsible For Addressing And Routing Of Packets Between Computers. It Does Not Guarantee Delivery And Does Not Give Acknowledgement Of Packets That Are Lost Or Sent Out Of Order As This Is The Responsibility Of Higher Layer Protocols Such As TCP.


    A Universal Naming Convention (UNC) Is Used To Allow The Use Of Shared Resources Without Mapping A Drive To Them. The UNC Specifies A Path Name And Has The Form:


    If I Have A Linux Server Called "Linux3" With A Folder Named "Downloads" With A File Called "Readme.Txt" In The Folder, The UNC Is:



  • Decomposition Of The Initial Information Flow Into Packets Of Standardized Size, And Reassembling At The Destination.

  • Routing Of A Packet Through Successive Networks, From The Source Machine To The Destination Identified By Its IP Address.

  • Transmitted Packets Are Not Guaranteed To Be Delivered (Datagram Protocol).

  • The IP Protocol Does Not Request For Connection (Connectionless) Before Sending Data And Does Not Make Any Error Detection.


  • Decompose The Initial Data (To Be Sent) Into Datagrams.

  • Each Datagram Will Have A Header Including, The IP Address And The Port Number Of The Destination.

  • Datagrams Are Then Sent To Selected Gateways, E.G IP Routers, Connected At The Same Time To The Local Network And To An IP Service Provider Network.



    UDP - A Connectionless, Datagram Service That Provides An Unreliable, Best-Effort Delivery.

    ICMP - Internet Control Message Protocol Enables Systems On A TCP/IP Network To Share Status And Error Information Such As With The Use Of PING And TRACERT Utilities.

    SMTP - Used To Reliably Send And Receive Mail Over The Internet.

    FTP - File Transfer Protocol Is Used For Transferring Files Between Remote Systems. Must Resolve Host Name To IP Address To Establish Communication. It Is Connection Oriented (I.E. Verifies That Packets Reach Destination).

    TFTP - Same As FTP But Not Connection Oriented.

    ARP - Provides IP-Address To MAC Address Resolution For IP Packets. A MAC Address Is Your Computer's Unique Hardware Number And Appears In The Form 00-A0-F1-27-64-E1 (For Example). Each Computer Stores An ARP Cache Of Other Computers ARP-IP Combinations.

    POP3 - Post Office Protocol. A POP3 Mail Server Holds Mail Until The Workstation Is Ready To Receive It.

    IMAP - Like POP3, Internet Message Access Protocol Is A Standard Protocol For Accessing E-Mail From Your Local Server. IMAP (The Latest Version Is IMAP4) Is A Client/Server Protocol In Which E-Mail Is Received And Held For You By Your Internet Server.

    TELNET - Provides A Virtual Terminal Or Remote Login Across The Network That Is Connection-Based. The Remote Server Must Be Running A Telnet Service For Clients To Connect.

    HTTP - The Hypertext Transfer Protocol Is The Set Of Rules For Exchanging Files (Text, Graphic Images, Sound, Video, And Other Multimedia Files) On The World Wide Web. It Is The Protocol Controlling The Transfer And Addressing Of HTTP Requests And Responses.

    HTTPS - Signifies That A Web Page Is Using The Secure Sockets Layer (SSL) Protocol And Is Providing A Secure Connection. This Is Used For Secure Internet Business Transactions.

    NTP - Network Time Protocol Is A Protocol That Is Used To Synchronize Computer Clock Times In A Network Of Computers.

    SNMP - Stands For Simple Network Management Protocol And Is Used For Monitoring And Status Information On A Network. SNMP Can Be Used To Monitor Any Device That Is SNMP Capable And This Can Include Computers, Printers, Routers, Servers, Gateways And Many More Using Agents On The Target Systems. The Agents Report Information Back To The Management Systems By The Use Of “Traps” Which Capture Snapshot Data Of The System. This Trap Information Could Be System Errors, Resource Information, Or Other Information. The SNMPV2 Standard Includes Enhancements To The Snmpv1 SMI-Specific Data Types, Such As Including Bit Strings, Network Addresses, And Counters. In Snmpv3 Security Was Addressed. Because All Of The Trap Information Sent Was In Clear Text, A Malicious Person Could Also Pull Any Monitoring Information Being Sent And Collected For Operational Purposes Off The Wire.

    SESSION INITIATION PROTOCOL (SIP): Service Providers Are Deploying Converged Voice-And-Data Services Based On Session Initiation Protocol (SIP) To Meet The Demands Of A Changing Business Environment, To Attract New Customers, And To Add To Their Portfolio Of Revenue-Generating Services. With Its Foundation In Internet Protocols, SIP Provides The Ability To Integrate Traditional Voice Services With Web-Based Data Services, Including Self-Based Provisioning, Instant Messaging, Presence, And Mobility Services.

    Cisco Is Enabling The Advance Of New Communications Services With A Complete SIP-Enabled Portfolio Including IP Phones And Analog Telephone Adaptors, Packet Voice Gateways, Proxy Servers, Call Control And Signaling, And Firewalls. These Products Are Available Today. Only Cisco Is Dedicated To Providing Ubiquitous And Seamless Protocol Interoperability In Its Packet Voice Solutions, And Cisco Solutions Support A Variety Of Call Control And Standard Protocols Including H.323, Media Gateway Control Protocol (MGCP), And SIP That Can Co-Exist In The Same Customer Network.

    The Protocol Can Be Used For Creating, Modifying And Terminating Two-Party (Unicast) Or Multiparty (Multicast) Sessions Consisting Of One Or Several Media Streams. The Modification Can Involve Changing Addresses Or Ports, Inviting More Participants, Adding Or Deleting Media Streams, Etc.

    RTP – Real-Time Transport Protocol Is The Audio And Video Protocol Standard Used To Deliver Content Over The Internet. RTP Is Used In Conjunction With Other Protocols Such As H.323 And RTSP.

    IGMP – Internet Group Management Protocol is used to manage Internet Protocol multicast groups. IP hosts and adjacent multicast routers use IGMP to establish multicast group memberships. IGMP is only needed for IPv4 networks, as multicast is handled differently in IPv6 networks.

    TLS - Transport Layer Security is a cryptographic protocol that provides security for communications over networks such as the Internet. TLS and SSL encrypt the segments of network connections at the Transport Layer end-to-end. Several versions of the protocols are in wide-spread use in applications like web browsing, electronic mail, Internet faxing, instant messaging and voice-over-IP (VoIP).


    Ports Are What An Application Uses When Communicating Between A Client And Server Computer. Some Common Ports Are:


    FTP                   TCP            20,21
    SSH                   TCP            22
    TELNET            TCP            23
    SMTP                TCP           25
    DNS                  TCP/UDP   53
    DHCP               UDP            67
    TFTP                UDP           69
    HTTP                TCP            80
    POP3                TCP            110
    NTP                   TCP           123
    IMAP4               TCP            143
    SNMP                 UDP           161
    HTTPS               TCP             443


    IPv4 - Every IP Address Can Be Broken Down Into 2 Parts, The Network ID(Netid) And The Host ID. All Hosts On The Same Network Must Have The Same Netid. Each Of These Hosts Must Have A Hostid That Is Unique In Relation To The NETID. IP Addresses Are Divided Into 4 Octets With Each Having A Maximum Value Of 255. We View Ipv4 Addresses In Decimal Notation Such As, But It Is Actually Utilized As Binary Data.


    CLASS        RANGE:

    A     1      -   126
    B     128   -   191
    C     192   -   223

    NOTE: Is Reserved For LOOPBACK Testing On The Local System And Is Not Used On Live Systems.


    IPv6 - The Previous Information On TCP/IP Has Referred To Ipv4, However, This Addressing Scheme Has Run Out Of Available IP Addresses Due To The Large Influx Of Internet Users And Expanding Networks. As A Result, The Powers That Be Had To Create A New Addressing Scheme To Deal With This Situation And Developed Ipv6.

    This New Addressing Scheme Utilizes A 128 Bit Address (Instead Of 32) And Utilizes A Hex Numbering Method In Order To Avoid Long Addresses Such As The Hex Address Format Will Appear In The Form Of 3FFE:B00:800:2::C

    MAC ADDRESSING - Also Known As Hardware Address Or Ethernet Address, A MAC Address Is A Unique Code Assigned To Most Networking Hardware. The Hardware Is Assigned A Unique Number By The Manufacturer And The Address Is Permanently Assigned To The Device. MAC Addresses Are In A 48-Bit Hexidecimal Format Such As 00:2f:21:C1:11:0a. They Are Used To Uniquely Identify A Device On A Network, And For Other Functions Such As For Being Authenticated By A DHCP Server.


    SUBNETTING: IP Addresses Can Be Class A, B Or C.

    CLASS A ADDRESSES Are For Networks With A Large Number Of Hosts. The First Octet Is The NETID And The Three (3) Remaining Octets Are The HOSTID.

    CLASS B ADDRESSES Are Used In Medium To Large Networks With The First 2 Octets Making Up The NETID And The Remaining 2 Are The HOSTID.

    CLASS C ADDRESSES Is For Smaller Networks With The First 3 Octets Making Up The NETID And The Last Octet Comprising The HOSTID. The Network ID And The Host ID Are Determined By A Subnet Mask.


    Class       Default Subnet    Subnets   Hosts Per Subnet

    Class A                 126          16,777,214.

    Class B            16,384        65,534.

    Class C        2,097,152    254

    What If You Wanted More Than One Subnet? Subnetting Allows You To Create Multiple Logical Networks That Exist Within A Single Class A, B, Or C Network. If You Don't Subnet, You Will Only Be Able To Use One Network From Your Class A, B, Or C Network. When Subnetting Is Employed, The Multiple Networks Are Connected With A Router Which Enables Data To Find Its Way Between Networks. On The Client Side, A Default Gateway Is Assigned In The TCP/IP Properties. The Default Gateway Tells The Client The IP Address Of The Router That Will Allow Their Computer To Communicate With Clients On Other Networks.


    The Original TCP/IP Addressing Method Described Above Was Called Classful Addressing Which Worked By Dividing The IP Address Space Into Chunks Of Different Sizes Called Classes.

    Classless Addressing Is Referred To As Classless Inter-Domain Routing (CIDR) And Is Done By Allocating Address Space To Internet Service Providers And End Users On Any Address Bit Boundary, Instead Of On 8-Bit Segments. So Does Not Have To Use The Standard Subnet Mask Of Which Makes A Class B Address Space And Which Also Puts It On The Same Network As Using The Subnet Mask Of (With Classful Addressing, Our Example Has 172.16 As The Network Name And The 50.0 And 51.0 Ranges Are Both Part Of The Same Host Naming Convention).

    Instead, By Using Classless Addressing Puts These Systems On A Different Network Than Because The Network Names Here Are 172.16.50 And 172.16.51 Which Are Different.

    NAT - NAT stands for Network Address Translation And is a commonly used IP translation and mapping technology. Using a device (such as a router) or piece of software that implements NAT allows an entire home or office network to share a single internet connection over a single IP address. A single cable modem, DSL modem, or even 56k modem could connect all the computers to the internet simultaneously.

    Additionally, NAT keeps your home network fairly secure from hackers. NAT is built in to the most common Internet Connection Sharing technologies.

    PAT – Port Address Translation Is a feature of a network device that translates TCP or UDP communications made between hosts on a private network and hosts on a public network. It allows a single public IP address to be used by many hosts on a private network.

    SNAT – Secure Network Address Translation an extension of the standard Network Address Translation (NAT) service. SNAT is done through one to one IP address translation of one internal IP address to one external IP address where NAT is effectively one external address to many internal IP addresses.

    DHCP - Dynamic Host Configuration Protocol provides a solution that automatically assigns IP addresses to computers on a network. When a client is configured to receive an IP address automatically, It will send out a broadcast to the DHCP server requesting an address.


  • Prevents Users From Making Up Their Own IP Addresses.
  • Prevents Incorrect Gateway Or Subnet Masks From Being Entered.
  • Decreases Amount Of Time Spent Configuring Computers Especially In Environments Where Computers Get Moved Around All The Time.

    APIPA – Stands For Automatic Private Internet Protocol Addressing. Client Systems That Are Configured For Automatic IP Address Assignment / Dynamic IP Assignment Will Attempt To Use DHCP To Make A Request For An IP Address Lease For A Given Network. When The DHCP Server Is Unavailable The Service On The Client Will Automatically Configure The System With An APIPA IP Address In The Through Address Range With A Subnet Mask Of

    UNICAST - The Sending Of Information Packets To A Single Network Node. This Type Of Network Transmission Is Used Where A Private Or Unique Resource Such As Media Servers Are Being Requested For Two Way Connections That Are Needed To Complete The Network Communication. So In The Media Server Example, A Client System May Make The Request For Streaming Content From The Single Source And The Responding System May Leverage Unicast As Part Of The Response To The Session Request To Deliver The Content.

    MULTICAST – A Single Source Address Responding To Multiple Destination Addresses With Information To Be Sent. In A Media Server Example, The Single Source Address May Need To Send The Data To Multiple Clients; It Does This By Sending The Data With Multiple Destination IP Addresses. All The Clients That “See” This Network Traffic Will Check To See If It Is Meant For Them With The Supplied Information. If It Is Not The Client Does Not Receive The Data. If A Network Node Does See That The Data Is Intended For Them The Device Will Respond By Receiving The Packet.

    BROADCAST – Traffic Sent Out From A Network Node That Will Reach Every Other Node On The Subnet / BROADCAST DOMAIN Because The Message Is Sent With The Intent Of Reaching All Nodes. The Network Node That Is Sending The Traffic Will Use The Broadcast Address For That Subnet And Every Device In That Broadcast Domain Will Receive The Broadcast Information. Generally The Broadcast Address Is The Last IP Address Of That Segment.

    As An Example, In The IP Address Range Of This Broadcast Address Would Be And The Traffic Would Reach All Available Nodes On The Subnet. Additionally Could Be Used Which Is The Broadcast Address Of The Zero Network ( Internet Protocol Standards Outline That The Zero Network Stands For The Local Network So Only Those Node On The Local Network Would Hear The Broadcast Traffic Across The Address.

    BROADCAST DOMAINIs A Logical Division Of A Computer Network, In Which All Nodes Can Reach Each Other By Broadcast At The Data Link Layer. A Broadcast Domain Can Be Within The Same LAN Segment Or It Can Be Bridged To Other LAN Segments.

    In Terms Of Current Popular Technologies: Any Computer Connected To The Same Ethernet Repeater Or Switch Is A Member Of The Same Broadcast Domain. Further, Any Computer Connected To The Same Set Of Inter-Connected Switches/Repeaters Is A Member Of The Same Broadcast Domain. Routers And Other Higher-Layer Devices Form Boundaries Between Broadcast Domains.

    This Is As Compared To A Collision Domain, Which Would Be All Nodes On The Same Set Of Inter-Connected Repeaters, Divided By Switches And Learning Bridges. Collision Domains Are Generally Smaller Than, And Contained Within, Broadcast Domains.

    While Some Layer Two Network Devices Are Able To Divide The Collision Domains, Broadcast Domains Are Only Divided By Layer 3 Network Devices Such As Routers Or Layer 3 Switches.

    A COLLISION DOMAIN - IS A Physical Network Segment Where Data Packets Can Collide With One Another When Being Sent On A Shared Medium, In Particular, When Using Early Versions Of The Ethernet Computer Networking Protocol. A Network Collision Occurs When More Than One Device Attempts To Send A Packet On A Network Segment At The Same Time. Collisions Are Resolved Using Carrier Sense Multiple Access Or A Variant Thereof In Which The Competing Packets Are Discarded And Re-Sent One At A Time. This Becomes A Source Of Inefficiency In The Network.

    This Situation Is Typically Found In A Hub Environment Where Each Host Segment Connects To A Hub That Represents Only One Collision Domain And Only One Broadcast Domain. Collision Domains Are Also Found In Broadcast Wireless Networks Such As Those Using Wi-Fi Products. Only One Device In The Collision Domain May Transmit At Any One Time, And The Other Devices In The Domain Listen To The Network In Order To Avoid Data Collisions.

    Because Only One Device May Be Transmitting At Any One Time, Total Network Bandwidth Is Shared Among All Devices. Collisions Also Decrease Network Efficiency On A Collision Domain; If Two Devices Transmit Simultaneously, A Collision Occurs, And Both Devices Must Retransmit At A Later Time.

    Modern Networks Use A Network Switch To Eliminate Collisions. By Connecting Each Device Directly To A Port On The Switch, Each Port On A Switch Becomes Its Own Collision Domain. As Each Connection Is Full Duplex Link, No Transmissions Can Collide And The Possibility Of Collisions Is Eliminated.


    LINK STATE ROUTING PROTOCOLS – Are One Of The Two Main Classes Of Routing Protocols Used In Packet Switching Networks And Includes Protocols Such As Open Shortest Path First (Ospf) And Intermediate System To Intermediate System (Is-Is). The Link-State Protocol Is Performed On Every Router On The Network, Where Every Routing Node Constructs A Map Of The Connectivity To The Network By Showing Which Nodes Are Connected To Each Other. Each Router Calculates The Next Best Logical Hop From It To Every Possible Known Destination Which Forms The Node's Routing Table.

    OPEN SHORTEST PATH FIRST (OSPF) – Is A Dynamic Routing Protocol And Is Used On Internet Protocol (IP) Based Networks Of All Sizes – Large To Small. OSPF Is An Interior Gateway Protocol (IGP) That Routes IP Packets Within A Single Routing Domain And Was Designed To Support Variable-Length Subnet Masking (VLSM) And Classless Inter-Domain Routing (CIDR) Addressing.

    OSPF DEAD TIMERS:- The Dead Time Field Indicates The Amount Of Time Remaining That The Router Waits To Receive An OSPF Hello Packet From The Neighbor Before Declaring The Neighbor Down. On Broadcast And Point-To-Point Media, The Default Dead Interval Is 40 Seconds. On Non-Broadcast And Point-To- Multipoint Links, The Default Dead Interval Is 120 Seconds.

    INTERMEDIATE SYSTEM TO INTERMEDIATE SYSTEM (IS-IS) – A LINK STATE PROTOCOL That Operates By Forwarding Network Topology Information Throughout A Network Of Routers. Each Router Then Independently Builds A Picture Of The Network's Topology Based On The Data Received And The Best Topological Path Through The Network To The Destination. IS-IS Is An Interior Gateway Protocol (IGP) Typically Used On Larger Networks.

    DISTANCE-VECTOR ROUTING PROTOCOLS – Are One Of The Two Main Classes Of Routing Protocols Used In Packet Switching Networks And Includes Routing Information Protocol (RIP) And Interior Gateway Routing Protocol (IGRP). Uses Distance As One Factor And The Vector As The Other To Determine Against The Known Routing Tables To Deliver Data To Source And Destination Locations. Routers Using The Distance-Vector Routing Protocol Will Update Other Routers Of Topology Changes Periodically When A Change Is Detected In The Topology Of A Network.

    ROUTING INFORMATION PROTOCOL (RIPV1) – RIP Is A Distance-Vector Routing Protocol Using “Hop Count” As A Routing Metric. The Maximum Number Of Hops Allowed For RIP Is 15 Which Effectively Limits The Size Of Networks That RIP Can Support.

    ROUTING INFORMATION PROTOCOL (RIPV2) – Improved Upon Ripv1 By Having The Ability To Include Subnet Information With Its Updates Which Allows For Classless Inter-Domain Routing (CIDR) Support. The 30 Second Proactive Broadcast Has Been Eliminated In Favor Of Multicast Advertisements For Its Updates. The 15 Hop Count Limit Remains So That The Devices Are Backwards Compatible With Ripv1 Devices.

    BORDER GATEWAY PROTOCOL (BGP) – Is The Core Routing Protocol Of The Internet. It Maintains A Table Of IP Networks And The Data That Designates Where And How To Reach Each Network Through Autonomous Systems (AS). BGP Makes Routing Decisions Based On Path, Network Policies And / Or Rule Sets.

    ENHANCED INTERIOR GATEWAY ROUTING PROTOCOL (EIGRP) – A Proprietary Hybrid Protocol From Cisco That Is A Distance Vector Routing Protocol That Functions Like A Link State Routing Protocol. EIGRP Collects Information And Stores It In Three Tables; The Neighbor Table Which Stores The Information About Neighboring Routers, The Topology Table Which Contains Only The Information And Data Regarding The Routing Tables From Directly Connected Neighbors And The Routing Table Which Stores The Actual Routes To All Destinations.


    INTERIOR GATEWAY PROTOCOL (IGP) – Routing Protocol That Is Used Within An Autonomous System Which Is Sometimes Referred To As An Administrative Domain. One Type Of Interior Gateway Protocol Are The Distance-Vector Routing Protocols Such As Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP) And Enhanced Interior Gateway Routing Protocol (EIGRP). Another Type Are The Link-State Routing Protocols Such As Open Shortest Path First (OSPF) And Intermediate System To Intermediate System (IS-IS)

    EXTERIOR GATEWAY PROTOCOL (EGP) – Routing Protocol That Is Used Across Different Autonomous Systems / Administrative Domains. It Was The Routing Protocol Leveraged For Internet Connected Devices In The Early 1980s. Border Gateway Protocol (BGP) Is The Replacement Standard For Internet Routing Over EGP.

    STATIC ROUTER UPDATES – A Router With Manually Configured Routing Tables. For These Types Of Devices, A Network Administrator Will Manually Build And Make Updates To The Routing Table For All Routes In The Administrative Domain. Static Routers Are Best Suited For Small Internetworks; Due To The Need Of The Manual Administration, They Do Not Scale Well To Large Networks Where Routing Information Is Often Changed, Updated And Appended. Static Routers Are Not Fault Tolerant Because When Another Network Device Goes Down The Manually Input Information May Not Necessarily Provide Alternate Pathing To A Destination Which Makes It Unreachable (Unless Quick, Manual Administrative Updates Are Made.)

    DYNAMIC ROUTER UPDATES – A Router With Dynamically Configured Routing Tables. This Type Of Automatic Configuration Is Made Up Of Routing Tables That Are Built And Maintained By Ongoing Communication Between The Routers Only (By Default – This Does Not Include Initial Setup And Configuration Or Administrative Needs For A Persistent Route Configuration). Dynamic Routing Is Fault Tolerant; If A Router Or Link Goes Down, The Routers Sense The Change In The Network Topology When The “Learned Route” Expires In The Routing Table And Cannot Be Renewed Due To The Outage. This Change Is Then Disseminated To Other Routers So That All The Routers “Learn” Of The Network Changes. Routing Information Protocol (RIP) And Open Shortest Path First (OSPF) Routing Protocols For IP And RIP For IPX Are Some Of Examples Of Protocols That Can Be Used For These Dynamic Updates.

    NEXT HOP – Defined As The Next Place That A Data Packet Needs To Go. In Most Cases, Routers Do Not Need All Of The Information Regarding Where The Originating Source Of The Data Transmission Was. In Most Cases Routers Just Need To Know Where There Data Needs To Go Next And The “Next” Referred To As The “Next Hop” Because All They Are Trying To Do Is Deliver It To The Specified Destination IP Address That Is Included In The Header Information Of The Data Being Sent. If That Router Is The Last Hop And Can Deliver It To The Specified IP Address It Does Otherwise It Refers To Its Routing Tables To Figure Out Which Router To Hand It Off To In The Effort To Get The Data Packet Where It Needs To Go.

    ROUTING TABLES – Sometimes Referred To As A Routing Information Base (RIB), Is The Database Information That Stores All The Rout Information For The Routing Network Devices. The Routing Table Holds The Route Information Regarding The Topology Of The Network Immediately Around The Device To Other Network Destinations And It Will Often Include The Metric / Cost Associated For The Route.


  • Network Route.
  • Host Route.
  • And The Default Route.

    THE NETWORK ROUTE Is Route To A Specific Network ID On The Network.

    The Host Route Is A Route To A Specific Network Address.

    A DEFAULT ROUTE Is The Path Used If A Physical Router Or Other Network Routing Device Cannot Find A Route For The Specified Destination.

    CONVERGENCE – Achieved When All Of The Available Topology Information From Routing Devices Have Been Passed Along To All Of The Other Deceives In Totality And All When The Information Gathered Is Not In A Contradiction State To Any Other Router's Informed Topology Information. When All Of The Network Routing Devices "Agree" On What The Network Topology Looks Like It Is Said To Have Full Convergence.

    WIRELESS ACCESS POINT - A Wireless Access Point Is A Radio Frequency Transceiver Which Allows Your Wireless Devices To Connect To A Network. The WAP Usually Connects To A Wired Network, And Can Relay Data Between The Wireless Devices (Such As Computers Or Printers) And Wired Devices On The Network. A Wireless Access Point Will Support Up To 32 Wireless Devices. The Range Of The Wireless Signal Depends Greatly On Obstructions Such As Walls.


    Wireless Networks Allow Computers To Comunicate Without The Use Of Cables Using IEEE 802.11 Standards, Also Known As Wi-Fi. A Connection Is Made From A Device, Which Is Usually A PC Or A Laptop With A Wireless Network Interface Card (NIC), And An Access Point (AP), Which Acts As A Bridge Between The Wireless Stations And Distribution System (DS) Or Wired Networks. An 802.11 Wireless Network Adapter Can Operate In Two Modes,Ad-Hoc And Infrastructure. In Infrastructure Mode, All Your Traffic Passes Through A Wireless ‘Access Point’. In Ad-Hoc Mode Your Computers Talk Directly To Each Other And Do Not Need An Access Point.



    802.11a     54 mbps     100 ft     5 GHz

    802.11b     11 mbps     300 ft     2.4 GHz

    802.11g     54 mbps     300 ft     2.4 GHz

    802.11n     540 mbps    600 ft     5 GHz and/or 2.4 GHz



    When We Talk About Local Area Network (Lan) Technology The Ieee 802 Standard May Be Heard. This Standard Defines Networking Connections For The Interface Card And The Physical Connections, Describing How They Are Done. The 802 Standards Were Published By The Institute Of Electrical And Electronics Engineers (Ieee). The 802.3 Standard Is Called Ethernet, But The Ieee Standards Do Not Define The Exact Original True Ethernet Standard That Is Common Today. There Is A Great Deal Of Confusion Caused By This. There Are Several Types Of Common Ethernet Frames. Many Network Cards Support More Than One Type.

    The Ethernet Standard Data Encapsulation Method Is Defined By Rfc 894. Rfc 1042 Defines The Ip To Link Layer Data Encapsulation For Networks Using The Ieee 802 Standards. The 802 Standards Define The Two Lowest Levels Of The Seven Layer Network Model And Primarily Deal With The Control Of Access To The Network Media. The Network Media Is The Physical Means Of Carrying The Data Such As Network Cable.


  • IEEE 802.1 – Internetworking
  • IEEE 802.2 - Logical Link Control *.
  • IEEE 802.3 - Ethernet Or Csma/Cd, Carrier-Sense Multiple Access With Collision Detection Lan *.
  • IEEE 802.4 - Token-Bus Lan *.
  • IEEE 802.5 - Token Ring Lan *.
  • IEEE 802.6 - Metropolitan Area Network (Man) .
  • IEEE 802.7 - Broadband Technical Advisory Group.
  • IEEE 802.8 - Fiber-Optic Technical Advisory Group.
  • IEEE 802.9 - Integrated Voice/Data Networks.
  • IEEE 802.10 - Network Security.
  • IEEE 802.11 - Wireless Networks.
  • IEEE 802.12 - Demand Priority Access Lan, 100 Base Vg-Anylan.

    *The Ones With Stars Should Be Remembered In Order For Network Certification Testing.


    There Are Various Methods Of Managing Access To A Network. If All Network Stations Tried To Talk At Once, The Messages Would Become Unintelligible, And No Communication Could Occur. Therefore A Method Of Being Sure That Stations Coordinate The Sending Of Messages Must Be Achieved.



    Carrier-Sense Multiple Access With Collision Avoidance (CSMA/CA).


    In The Early Days Of Ethernet, When Two Hosts Would Send Packets At The Same Time, A Collision Would Occur. A Standard Had To Be Created That Would Have The Hosts Follow Rules Relating To When They Could Send Data And When They Could Not. This Standard Is Carrier Sense Multiple Access With Collision Detection, Referred To As CSMA/CD.

    CSMA/CD Forces Computers To “Listen” To The Wire Before Sending In Order To Make Sure That No Other Host On The Wire Is Sending. If A Collision Is Detected, Both Of The Senders Will Send A Jam Signal Over The Ethernet. This Jam Signal Indicates To All Other Devices On The Ethernet Segment That There Has Been A Collision, And They Should Not Send Data Onto The Wire.


    Bonding (AKA Link Aggregation, Port Trunking, Etherchannel, Etc.) - Uses Multiple Network Cables/Ports In Parallel To Increase The Link Speed Beyond The Limits Of Any One Single Cable Or Port, And To Increase The Redundancy For Higher Availability.

  • Token Passing - A Token Is Passed From One Computer To Another, Which Provides Transmission Permission.

  • Demand Priority - Describes A Method Where Intelligent Hubs Control Data Transmission. A Computer Will Send A Demand Signal To The Hub Indicating That It Wants To Transmit. The Hub Sill Respond With An Acknowledgement That Will Allow The Computer To Transmit. The Hub Will Allow Computers To Transmit In Turn. An Example Of A Demand Priority Network Is 100vg-Anylan (IEEE 802.12). It Uses A STAR-BUS TOPOLOGY.

  • Polling - A Central Controller, Also Called The Primary Device Will Poll Computers, Called Secondary Devices, To Find Out If They Have Data To Transmit. Of So The Central Controller Will Allow Them To Transmit For A Limited Time, Then The Next Device Is Polled.

    Token Passing Performs Better When The Network Has A Lot Of Traffic, While Ethernet Which Uses CSMA/CD Is Generally Faster But Loses Performance When The Network Has A Lot Of Traffic. CSMA/CD Is Basically A Method That Allows Network Stations To Transmit Any Time They Want. They, However, Sense The Network Line And Detect If Another Station Has Transmitted At The Same Time They Did. This Is Called A Collision. If A Collision Happened, The Stations Involved Will Retransmit At A Later, Randomly Set Time In Hopes Of Avoiding Another Collision.


  • WEP - Wired Equivalent Privacy Is A Security Encryption Algorithm That Is Easily Cracked. For This Reason, It Has Been Replaced By Other Technologies.

  • WPA - The Original WPA Standard Used TKIP, But Was Later Replaced By WPA2 Which Uses A More Secure AES-Based Algorithm. WPA Uses A 256 Bit Key To Encrypt Data. This Key May Be Entered Either As A String Of 64 Hexadecimal Digits, Or As A PASSPHRASE Of 8 To 63 Characters. It Is Susceptible To Brute Force Attacks When A Weak Passphrase Is Used.

  • RADIUS - Remote Authentication Dial In User Service (RADIUS) Is A Networking Protocol That Provides Centralized Authentication, Authorization, And Accounting (AAA) Management For Computers To Connect And Use A Network Service. RADIUS Is Often Used By Isps And Enterprises To Manage Access To The Internet Or Internal Networks, And Wireless Networks. Microsoft's Answer To Corporate Wireless Security Is The Use Of RADIUS Authentication Through Its Internet Authentication Services (IAS) Product.

  • TKIP - Temporal Key Integrity Protocol Was Designed As A Solution To Replace WEP Without Requiring The Replacement Of Legacy Hardware. TKIP Suffered From Similar Flaws As WEP And Has Been Replaced By More Secure Encryption Schemes.





    CAT3 - Unshielded Twisted Pair Capable Of Speeds Up To 10Mbit/S. Used With 10Base-T, 100Base-T4, And 100Base-T2 Ethernet.

    CAT4 - Unshielded Twisted Pair Capable Of Speeds Up To 20Mbit/S. Not Widely Used. Used With 10Base-T, 100Base-T4, And 100Base-T2 Ethernet.

    CAT5 - Unshielded Twisted Pair Capable Of Speeds Up To 100Mbit/S. May Be Used With 10Base-T, 100Base-T4, 100Base-T2, And 100Base-TX Ethernet.

    CAT5e - Enhanced Cat 5 Is Similar To CAT5, But Exceeds Its Performance. Improved Distance Over Previous Categories From 100m To 350m. May Be Used For 10Base-T, 100Base-T4, 100Base-T2, 100basetx And 1000Base-T Ethernet.

    One Of The Least Expensive Network Media Is The Category-5 Enhanced (Cat-5e) Cable. Its Low Cost Has Made Cat-5e Cabling A Very Popular Choice For Wired Networks. One Drawback, However, Is That There Is A Limit To The Useful Length Of A Cat-5e Cable.

    CAT6 - Can Transmit Data Up To 220m At Gigabit Speeds. It Has Improved Specifications For NEXT (Near End Cross Talk), PSELFEXT (Power Sum Equal Level Far End Cross Talk), And Attenuation. Cat 6 Is Backward Compatible With Lower Category Grades And Supports The Same Ethernet Standards As Cat 5e.CATEGORY 6 CABLE, Also Known As Cat6, Is Capable Of Achieving High Speeds Of Data Transmission, Proving Useful For Networking When Large Files Will Be Transferred Often. Care Must Be Exercised When Pulling Cat6 Cable To Avoid Damaging The Cable. Whether Pulling Through Walls Or Pipes, Known As Conduit, The Nuts Of Bolts Of How To Pull The Cable Will Vary.

    However, There Are Some Basic Things To Remember That Will Aid In Any Cat6 Cable Pull.

    MULTIMODE FIBER Multimode Fibers Have Large Cores. They Are Able To Carry More Data Than Single Mode Fibers Though They Are Best For Shorter Distances Because Of Their Higher Attenuation Levels.

    SINGLE MODE FIBER - Single Mode Fibers Have A Small Glass Core. Single Mode Fibers Are Used For High Speed Data Transmission Over Long Distances. They Are Less Susceptible To Attenuation Than Multimode Fibers.

    RG59 And RG6 These Are Both Shielded Coaxial Cables Used For Broadband Networking, Cable Television, And Other Uses.

    SERIAL A SERIAL CABLE Is A Cable That Can Be Used To Transfer Information Between Two Devices Using Serial Communication, Often Using The RS-232 Standard. Typically Use D-Subminiature Connectors With 9 Or 25 Pins. Cables Are Often Unshielded, Although Shielding Cables May Reduce Electrical Noise Radiated By The Cable.

    SHIELDED TWISTED PAIR (STP) - Differs From UTP In That It Has A Foil Jacket That Helps Prevent Cross Talk. Cross Talk Is Signal Overflow From An Adjacent Wire.

    EMI - ELECTRICAL DEVICES Such As Printers, Air Conditioning Units, And Television Monitors Can Be Sources Of Electromagnetic Interference, Or EMI. Some Types Of Network Media Have More Resistance To EMI Than Others. Standard UTP Cable Has Minimal Resistance To EMI, While Fiber Optic Cable Is Highly Resistant.

    PLENUM GRADE CABLING - Is Required If The Cabling Will Be Run Between The Ceiling And The Next Floor (This Is Called The Plenum). Plenum Grade Cabling Is Resistant To Fire And Does Not Emit Poisonous Gasses When Burned.


  • HALF DUPLEX - Half Duplex Means That signals can be passed in either direction, but not in both simultaneously.

  • FULL DUPLEX - Full Duplex Means that signals can be passed in either direction simultaneously.


    BNC - This Connector Has Found Uses With Both Broadcast Television Equipment And Computer Networks. With Regards To Networking, This Connector Was Used On Early 10Base-2 (Thinnet) Ethernet Networks. It Has A Center Pin Connected To The Center Coaxial Cable Conductor And A Metal Tube Connected To The Outer Cable Shield. A Rotating Ring Outside The Tube Locks The Cable To The Female Connector.

    RJ11 - Short For Registered Jack-11, A Four Or Six-Wire Connector Used Primarily To Connect Telephone Equipment In The United States (POTS). The Cable Itself Is Called Category 1 (Cat 1) And Is Used For Dial-Up Connections. Modems Have Rj-11 Jacks That Connect Them To The Wall Outlet.

    RJ45 - Short For Registered Jack-45, It Is An Eight-Wire Connector Used Commonly To Connect Devices On Ethernet Lans. RJ-45 Connectors Look Similar To RJ-11 Connectors Used For Connecting Telephone Equipment, But They Are Larger.

    Is A Type Of Registered Jack. As A Registered Jack, Telephone RJ45 Specifies The Physical Male And Female Connectors As Well As The Pin Assignments Of The Wires In A Telephone Cable. The Original RJ45 Uses A Special Keyed 8P2C Modular Connector, With Pins 5 And 4 Wired For Tip And Ring Of A Single Telephone Line And Pins 7 And 8 Connected To A Programming Resistor. It Is Used With A High Speed Modem.

    Before The Name RJ45 Was Used To Refer To Computer Networking Connectors, RJ45 Was Originally A Telephone-Only Standard. Telephone Installers Who Wired Telephone RJ45 Jacks Were Familiar With The Pin Assignments Which Were Part Of The RJ45 Standard. However, Nearly Identical Physical Connectors For Computer Networking Became Ubiquitous, And Informally Inherited The Name RJ45 Due To The Overwhelming Similarity. While Telephone RJ45 Uses A "Keyed" Variety Of The 8P Body, Meaning It May Have An Extra Tab With Which A Computer RJ45 Connector Is Unable To Mate, The Visual Difference Compared To An Ethernet 8P Is Subtle.

    The Only Other Difference Is The Presence Of Extra Conductors In The Cable, Which Cannot Be Seen Without Very Close Inspection. True Telephone RJ45 Connectors Are A Special Variant Of 8P2C, Meaning Only The Middle 2 Positions Have Conductors In Them, While Pins 7 And 8 Are Shorting A Programming Resistor. Computer "RJ45" Is 8P8C, With All Eight Conductors Present.

    Understandably, Because Telephone RJ45 8P Connectors Never Saw Wide Usage And Computer 8P Connectors Are Quite Well Known Today, RJ45 Is (Erroneously) Used Almost Exclusively To Refer To Ethernet-Type Computer Connectors. Electronics Catalogs Not Specialized To The Telephone Industry Advertise 8P8C Modular Connectors As "RJ45." Virtually All Electronic Equipment Which Uses An 8P8C Connector (Or Possibly Any 8P Connector At All) Will Document It As An "RJ45" Connector. In Common Usage, RJ45 Also Refers To The Pin Assignments For The Attached Cable, Which Are Actually Defined In Wiring Standards Such As TIA/EIA-568-B.

    ST - The ST Connector Is A Fiber Optic Connector Which Uses A Plug And Socket Which Is Locked In Place With A Half-Twist Bayonet Lock. The ST Connector Was The First Standard For Fiber Optic Cabling. ST Connectors Are Half-Duplex.

    SC - The SC Connector Is A Fiber Optic Connector With A Push-Pull Latching Mechanism Which Provides Quick Insertion And Removal While Also Ensuring A Positive Connection. SC Connectors Are HALF - DUPLEX.

    LC - The LC Connector Is Just Like A SC Connector Only It Is Half The Size. Like SC Connectors, LC Connectors Are HALF-DUPLEX.

    RS232 - A Standard For Serial Binary Data Interconnection Between A DTE (Data Terminal Equipment) And A DCE (Data Communication Equipment). Commonly Found In Use With Bar Code Scanners, Measuring Tools, And Laboratory Instruments Are Designed To Interface To A Computer Using A Standard RS232 Serial Cable Connection. Many Of These Uses Are Being Replaced With USB Enabled Devices. The Connector Is A DB-9 Or DB-25 Connector.


    STAR - The Star Topology Uses Twisted Pair (10baset Or 100baset) Cabling And Requires That All Devices Are Connected To A Hub. Advantages Are Centralized Monitoring, And Failures Do Not Affect Others Unless It Is The Hub, Easy To Modify. The Disadvantage Is That The Hub Is A Single Point Of Failure. If It Goes Down, There Are No Communications Possible.

    MESH - In A True Mesh Topology Every Node Has A Connection To Every Other Node In The Network. A Full Mesh Provides Redundancy In Case Of A Failure Between Links, But Is Impractical Due The Complexity And The Expensive Amount Of Cabling Required.

    BUS - This Topology Is An Old One And Essentially Has Each Of The Computers On The Network Daisy-Chained To Each Other. Packets Must Pass Through All Computers On The Bus. This Type Is Cheap, And Simple To Set Up, But Causes Excess Network Traffic, A Failure May Affect Many Users, And Problems Are Difficult To Troubleshoot.

    RING - A Ring Topology Has A Physical And Logical Ring And Is Used On SONET And FDDI Networks (Note That Token Ring Networks Are Actually A Hybrid Star Ring Topology). Any Station Can Send A Packet Around The Ring But Only The Station With The Token Can Do So. The Token Is Passed Around The Ring Giving All Stations An Opportunity To Communicate. This Is A Very Fast And Simple Network. However If Any Part Of The Ring Goes Down, The Entire LAN Goes Down. If There Is A Problem At A Station, It May Be Difficult To Locate It. Ring Networks Are Not Very Common.

    POINT TO POINT - This Topology Generally Refers To A Connection Restricted To Two Endpoints. Point-To-Point Is Sometimes Referred To As P2P (Not The Same As Peer-To-Peer File Sharing Networks), Or Pt2Pt, Or Variations Of This. Examples Of This Topology Include RS-232 Serial Connections As Well As Laser Network Connections Between Buildings.

    POINT TO MULTIPOINT - Also Known As P2MP, This Is A Method Of Communication Between A Series Of Receivers And Transmitters To A Central Location. The Most Common Example Of This Is The Use Of A Wireless Access Point That Provides A Connection To Multiple Devices.

    HYBRID - Hybrid Topologies Are Combinations Of The Above And Are Common On Very Large Networks. For Example, A Star Bus Network Has Hubs Connected In A Row (Like A Bus Network) And Has Computers Connected To Each Hub As In The Star Topology.


    568A And 568B - The Number 568 Refers To The Order In Which The Individual Wires Inside A CAT 5 Cable Are Terminated. The Only Difference Between The Two Standards Is That The Green And Orange Pins Are Terminated To Different Pins. There Is No Difference In Signal And Both The 568A And 568B Are Used As Patch Cords For Ethernet Connections.


    There Are Generally Three Main Types Of Networking Cables:

  • Straight-Through,
  • Crossover,
  • And Rollover Cables.

    Each Cable Type Has A Distinct Use, And Should Not Be Used In Place Of Another.

    STRAIGHT-THROUGH CABLES Are Primarily Used For Connecting Unlike Devices. A Straight-Through Cable Is Typically Used In The Following Situations:


    1. Connecting A Computer To A Router.
    2. Connecting A Computer To A Computer.
    3. Connecting A Router To A Router.
    4. Connecting A Switch To A Switch.
    5. Connecting A Hub To A Hub.


  • Switch-To-Switch.
  • PC To Router, PC To PC - Crossover.
  • Switch-To-Hub.
  • Hub-To-Hub.
  • Router-To-Router.
  • Router-To-Server.


    1. Connecting A Router To A Hub.
    2. Connecting A Computer To A Swtich.
    3. Connecting A LAN Port To A Switch, Hub, Or Computer.


  • Switch-To-Router / Router To Switch.
  • Switch-To-PC / PC To Switch.
  • Hub-To-PC.
  • Hub-To-Server.


    A STRAIGHT THROUGH CABLE USE Either The 568A Or 568B Wiring Standard And Is Used For Connecting Devices To Routers, Hubs, Switches, Etc.

    A CROSSOVER CABLE IS USE To Connect Computing Devices Together Directly (I.E. Connecting 2 Computers Directly Together).

    A CROSSOVER CABLE USE The 568A Standard On One End And 568B On The Other End.

    ROLLOVER - Rollover Cable (Also Known As Cisco Console Cable) Is A Type Of Null-Modem Cable That Is Most Commonly Used To Connect A Computer Terminal To A Router's Console Port. This Cable Is Typically Flat And Has A Light Blue Color. It Gets The Name Rollover Because The Pinouts On One End Are Reversed From The Other, As If The Wire Had Been Rolled Over And You Were Viewing It From The Other Side.

    LOOPBACK - A Loopback Cable Redirects The Output Back Into Itself And Is Used For Troubleshooting Purposes (Loopback Test). This Effectively Gives The NIC The Impression That It Is Communicating On A Network, Since Its Able To Transmit And Receive Communications.


    FRAME RELAY - Frame Relay Is A Secure, Private Network That Utilizes A Logical Path Or “Virtual Circuit” To Allocate Bandwidth For High Performance Transmissions. Frame Relay Is The Premier High-Speed Packet-Switching Protocol Communicating Data, Imaging, And Voice Between Multiple Locations. Frame Relay Is Available In A Range Of Bandwidths From 56 Kbps To Full T1 (1.54 Mbps).

    T-1/T-3 - A T-1 Is A Dedicated Phone Connection Supporting Data Rates Of 1.544Mbps. A T-1 Line Actually Consists Of 24 Individual Channels, Each Of Which Supports 64Kbits Per Second. Each 64Kbit/Second Channel Can Be Configured To Carry Voice Or Data Traffic. Most Telephone Companies Allow You To Buy Just Some Of These Individual Channels, Known As Fractional T-1 Access. T-1 Lines Are A Popular Leased Line Option For Businesses Connecting To The Internet And For Internet Service Providers (Isps) Connecting To The Internet Backbone. The Internet Backbone Itself Consists Of Faster T-3 Connections. T-1 Comes In Either Copper Or Fiber Optics.

    ATM - ATM Stands For Asynchronous Transfer Mode And Is A High-Speed, Packet-Switching Technique That Uses Short Fixed Length Packets Called Cells. ATM Can Transmit Voice, Video, And Data Over A Variable-Speed LAN And WAN Connections At Speeds Ranging From 1.544Mbps To As High As 622Mbps. ATM Is Capable Of Supporting A Wide Range Of Traffic Types Such As Voice, Video, Image And Data.

    SONET - SONET And SDH Are A Set Of Related Standards For Synchronous Data Transmission Over Fiber Optic Networks. SONET Is Short For Synchronous Optical Network And SDH Is An Acronym For Synchronous Digital Hierarchy. SONET Is The United States Version Of The Standard And SDH Is The International Version. SONET Defines A Base Rate Of 51.84 Mbps And A Set Of Multiples Of The Base Rate Known As "Optical Carrier Levels." (Ocx). Speeds Approaching 40 Gigabits Per Second Are Possible.

    ISDN - INTEGRATED SERVICES DIGITAL NETWORK (ISDN) Is Comprised Of Digital Telephony And Data-Transport Services Offered By Regional Telephone Carriers. ISDN Involves The Digitalization Of The Telephone Network, Which Permits Voice, Data, Text, Graphics, Music, Video, And Other Source Materials To Be Transmitted Over Existing Telephone Wires. There Are 2 Types Of ISDN Channels:

    B (BEARER) - Transfers Data At 64Kbps. An ISDN Usually Contains 2 B Channels For A Total Of 128kbps.

    D (DATA) - Handles Signalling At Either 16Kbps Or 64Kbps(Sometimes Limited To 56Kbps) Which Enables The B Channel To Strictly Pass Data.


    ISDN BRI    64kbps/channel    Twisted-pair

    ISDN PRI    1,544kbps    Twisted-pair

    POTS    Up to 56 Kbps     Twisted pair

    PSTN     64kbps/channel    Twisted-pair

    Frame Relay    56kbps-45mbps    Varies

    T-1    1.544 Mbps     Twisted-pair, coaxial, or optical fiber

    ADSL    256Kbps to 24Mbps (ADSL 2+)    Twisted-pair

    SDSL    1.544mbps    Twisted-pair

    VDSL    100mbps    Twisted-pair

    Cable modem    512 Kbps to 52 Mbps    Coaxial

    Satellite    1gbps (avg 1-5mbps)     Air

    T-3    44.736 Mbps     Twisted-pair, coaxial, or optical fiber

    OC-1    51.84 Mbps     Optical fiber

    OC-3    155.52 Mbps VOptical fiber

    Wireless     1gbps     Air

    ATM    10gbps     Optical fiber

    SONET    10gbps     Optical fiber

    PACKET AND CIRCUIT SWITCHING - Packet Switching Refers To Protocols In Which Messages Are Divided Into Packets Before They Are Sent. Each Packet Is Then Transmitted Individually And Can Even Follow Different Routes To Its Destination. Once All The Packets Forming A Message Arrive At The Destination, They Are Recompiled Into The Original Message. Most Modern Wide Area Network (WAN) Protocols, Including TCP/IP And Frame Relay Are Based On Packet-Switching Technologies.

    In Contrast, Normal Telephone Service Is Based On A Circuit-Switching Technology, In Which A Dedicated Line Is Allocated For Transmission Between Two Parties.

    Circuit-Switching Is Ideal When Data Must Be Transmitted Quickly And Must Arrive In

    The Same Order In Which It Is Sent. This Is The Case With Most Real-Time Data, Such As Live Audio And Video. Packet Switching Is More Efficient And Robust For Data That Can Withstand Some Delays In Transmission, Such As E-Mail Messages And Web Pages.


    ETHERNET - ETHERNET Is The Most Widely-Installed Local Area Network ( LAN) Technology. Specified In A Standard, IEEE 802.3, Ethernet Was Originally Developed By Xerox From An Earlier Specification Called Alohanet (For The Palo Alto Research Center Aloha Network) And Then Developed Further By Xerox, DEC, And Intel. Early Ethernet Networks Uses Coaxial Connections. The Most Common Types Currently Use Twisted Pair Cabling, However, Fiber Optic Cabling Is Becoming Much More Common As Standards And Speeds Increase. Below Are Some Of The Ethernet Standards:


    10Base-T   Category 3 or better UTP cable    RJ-45    100 meters (328 ft)     10 mbps

    100Base-TX    Cat 5 twisted pair    RJ-45    100 meters (328 ft)     100 mbps

    100Base-FX    Fiber Optic    ST, SC 2000 meters    100 mbps

    1000Base-T    CAT5e or higher    RJ-45    100 meters (328 ft)     1 gbps

    1000Base-LX Laser over fiber    SC     Up to 5000 meters     1 gbps

    1000Base-SX Short wavelength laser over fiber    SC    Up to 550 meters    1 gbps

    1000Base-CX Twinax or short haul copper    9-Pin shielded D-subminiature connector, or 8-pin ANSI fiber channel type 2 (HSSC) connector.     25 meters     1 gbps

    10GBASE-SR Shortwave laser over multi-mode fiber optics    LC, SC    300 meters    10 Gbps 10GBASE-LR Laser over single-mode fiber optics LC,     SC    2000 meters    10 Gbps

    10GBASE-ER Laser over either single or multi-mode fiber LC,     SC    40 kilometers     10 Gbps

    10GBASE-SW Shortwave laser over multi-mode fiber optics     LC, SC    300 meters     10 Gbps

    10GBASE-LW Laser over single-mode fiber optics LC, SC 2000 meters 10 Gbps

    10GBASE-EW Laser over either single or multi-mode fiber LC, SC 40 kilometers 10 Gbps

    10GBASE-T Cat 5e (or higher) twisted pair RJ-45 100 meters (328 ft) 10 Gbps


    PEER TO PEER - A Peer To Peer Network Is One In Which Lacks A Dedicated Server And Every Computer Acts As Both A Client And A Server. This Is A Good Networking Solution When There Are 10 Or Less Users That Are In Close Proximity To Each Other. A Peer To Peer Network Can Be A Security Nightmare, Because The People Setting Permissions For Shared Resources Will Be Users Rather Than Administrators And The Right People May Not Have Access To The Right Resources.

    More Importantly The Wrong People May Have Access To The Wrong Resources, Thus, This Is Only Recommended In Situations Where Security Is Not An Issue. P2P File Sharing Networks Work Under A Similar Architecture, However, There Are Differences Between Them And The LAN Networking Architecture.

    CLIENT/SERVER - This Type Of Network Is Designed To Support A Large Number Of Users And Uses Dedicated Server/S To Accomplish This. Clients Log In To The Server/S In Order To Run Applications Or Obtain Files. Security And Permissions Can Be Managed By 1 Or More Administrators Which Who Set Permissions To The Servers' Resources. This Type Of Network Also Allows For Convenient Backup Services, Reduces Network Traffic And Provides A Host Of Other Services That Come With The Network Operating System.

    VPN - A Virtual Private Network Is One That Uses A Public Network (Usually The Internet) To Connect Remote Sites Or Users Together. Instead Of Using A Dedicated, Real-World Connection Such As Leased Line, A VPN Uses "Virtual" Connections Routed Through The Internet From The Company's Private Network To The Remote Site Or Employee.

    VLAN - A Virtual LAN Is A Local Area Network With A Definition That Maps Workstations On A Basis Other Than Geographic Location (For Example, By Department, Type Of User, Or Primary Application). The Virtual LAN Controller Can Change Or Add Workstations And Manage Load-Balancing And Bandwidth Allocation More Easily Than With A Physical Picture Of The LAN. Network Management Software Keeps Track Of Relating The Virtual Picture Of The Local Area Network With The Actual Physical Picture.


    VERTICAL CROSS CONNECT – Is A Location Within A Building Where Cables Originate And / Or Are Terminated, Reconnected Using Jumpers Or Pass Throughs Or Are Connected To Patch Panels Or Other Similar Devices Where The Locations Are From Upper Or Lower Floors In The Building. These Cables Could Be Of Multiple Different Types And Mediums Such As Phone Networks, Data Lines, Copper Based, Fiber Channel, Etc.

    HORIZONTAL CROSS CONNECT – Similar To Vertical Cross Connect Locations; These Are Within A Building Where Cables Originate And / Or Are Terminated But These Locations Are All On The Same Floor Or Building Level. As With Vertical Cross Connect Configurations, These Locations Can Be Of Multiple Different Network Types And Mediums.

    PATCH PANEL – Wall Or Rack Mounted Collection Of Data Connections Where All Of The Network Media Converges. These Rooms Are Generally Some Form Of Telecommunications Closet In A Facility And It Is Used To Connect All Of The Different Types Of Incoming And Outgoing Media Types On The LAN. When They All Span The Same Floor Of A Building They Are Sometimes Referred To As Horizontal Cross Connect Locations And When They Span Different Levels Of A Location / Different Floors Of A Building They Are Sometimes Referred To As Vertical Cross Connect Locations. The Main Patch Panel Room Will Often Be The Connection Point For The LAN To Be Connected To The WAN And / Or The Internet.

    66 BLOCK – Is A Legacy Type Of Punch Down Block Used To Connect Sets Of 22 Through 26 American Wire Gauge (AWG) Solid Copper Wire In A Telephone System. They Have A 25-Pair Standard Non-Split Capacity And Generally Are Unsuited For Traffic And Data Network Communications Above 10 Megabits Per Second (MBPS).

    MAIN DISTRIBUTION FRAME (MDF) – Is A Wire Distribution Frame For Connecting Equipment Inside A Facility To Cables And Subscriber Carrier Equipment Outside Of The Facility. One Example Of This Is Where All Of The Phone Cabling Inside A Facility Is Run To Planned Phone Locations (E.G. Offices) Back To The MDF. When The Local Telephone Company Makes The External Connections Then All Circuits Are Completed.

    INTERMEDIATE DISTRIBUTION FRAME (IDF) – Is Another Place Much Like A Horizontal Cross Connect Location Or A Vertical Cross Connect Location Where Network Administrators Can Physically Change The Network Media Around And Where They Can House Other Needed Network Equipment Such As Routers, Switches, Repeaters And So Forth.

    25 PAIR – Is A Grouping Of 25 Pairs Of Wires All Inside A Single Covering / Housing Or Outer Insulation Casing. It Is Best Suited For Telephone / Voice Cable Runs Rather Than Data Cable Runs And Is Generally Used As A Feeder Cable.

    100 PAIR – Is A Larger Cabling Segment To Its 25 Pair Cousin But Used In The Same Manner; All Of The 100 Pairs Of Wires Are Inside A Single Covering / Housing Or Outer Insulation Casing. It Is Best Suited For Telephone / Voice Cable Runs Rather Than Data Cable Runs And Is Generally Used As A Feeder Cable.

    110 BLOCK – Is The More Modern Replacement Of The Legacy 66 Block And Is Used As A Wiring Distribution Point For Wired Telephone Systems (Voice) And Other Types Of Wired Networking (Data). On One Side Of The Block Wires Are Punched Down Into RJ-11 Connectors For Voice And RJ-45 Connectors For Data Communications.

    DEMARC – Is The Point Of Operational And Administrative Control Change In A Network. One Example Of This Is The Main Distribution Frame (MDF) Point In A Facility. This Is Where The Wire Distribution Frame For Connecting Equipment Inside A Facility To Cables And Subscriber Carrier Equipment Outside Of The Facility Occurs And This Is Considered A Demarcation Point Of The Operational Control Of The Internal Systems Where It Changes Over To The Control Of The External Presence.

    DEMARC EXTENSION – where the end of the line of the external administrative control is extended beyond that actual endpoint. Example – you are one business inside of a large high rise building on the 15th floor only and the Main Distribution Frame (MDF) point is on the ground floor. Your responsibility probably ends at the Intermediate Distribution Frame (IDF) on your floor and the external administration (example – Phone Company) ends at the Main Distribution Frame (MDF) on the ground floor. The building administration owns all the cabling responsibility between the Main Distribution Frame (MDF) on the ground floor and your Intermediate Distribution Frame (IDF) on your floor. That cabling is effectively the Demarc Extension

    SMART JACK – Is A Network Connection Device That Is Used To Connect Your Internal Network To An External Service Provider Network. The Device Handles All Of The Code And Protocol Differences Between The Two Networks And Is Often The Actual Demarcation Point Between The Two Service Entities.

    WIRING INSTALLATION – Is The Physical Installation Of Internal Wiring In A Facility. This May Be The Pulls Of Copper Phone And Data Lines To The Running Of Fiber Optic Medium From The Different Cross Connect Locations.

    WIRING TERMINATION – Is The End Point Of Networked Cable Runs That Will Generally End Either In A Patch Panel Or A Jack Location In An Office. This Has Historically Been The Copper Wire Runs Associated With Phone Lines To The RJ-11 Jacks / Blocks To The Data Lines On The RJ-45 Connections. Wire Termination Is Also A Consideration On Fiber Optic Pulls As Well Which Requires A Higher Set Of Skill Level.


    HUB - A Physical Layer Network Device Used To Connect Multiple Ethernet Devices Together. Active Hubs Act As A Repeater And Boost The Signal In Order To Allow For It To Travel Farther, While Passive Hubs Simply Pass The Signal Through. Most Hubs Have An Uplink Port That Allows Them To Connect To Other Hubs, A Router, Or Other Network Devices.

    NETWORK REPEATER - A Physical Layer Device That Boosts Signals In Order To Allow A Signal To Travel Farther And Prevent Attenuation. Attentuation Is The Degradation Of A Signal As It Travels Farther From Its Origination. Repeaters Do Not Filter Packets And Will Forward Broadcasts. Both Segments Must Use The Same Access Method, Which Means That You Can't Connect A Token Ring Segment To An Ethernet Segment. Repeaters Can Connect Different Cable Types As Shown In The Image.

    Also A repeater connects two segments of your network cable. It retimes and regenerates the signals to proper amplitudes and sends them to the other segments. When talking about, ethernet topology, you are probably talking about using a hub as a repeater. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay which can affect network communication when there are several repeaters in a row. Many network architectures limit the number of repeaters that can be used in a row. Repeaters work only at the physical layer of the OSI network model.

    MODEM - The Modem Is A Device That Converts Digital Information To Analog By Modulating It On The Sending End And Demodulating The Analog Information Into Digital Information At The Receiving End. Most Modern Modems Are Internal, However, They Can Be Internal Or External. External Modems Are Connected To The Back Of The System Board Via A RS-232 Serial Connection. Internal Modems Are Installed In One Of The Motherboard's PCI Or ISA Expansion Slots Depending On The Modem. The Modem Contains An RJ-11 Connection That Is Used To Plug In The Telephone Line.


  • SIMPLEX - Signals Can Be Passed In One Direction Only.

  • HALF DUPLEX - Half Duplex Means That Signals Can Be Passed In Either Direction, But Not In Both Simultaneously. Half-Duplex Modems Can Work In Full-Duplex Mode.

  • FULL DUPLEX - Full Duplex Means That Signals Can Be Passed In Either Direction Simultaneously.

    MODEMS Can Also Be Classified By Their Speed Which Is Measured By The BAUD Rate. One Baud Is One Electronic State Change Per Second. Since A Single State Change Can Involve More Than A Single Bit Of Data, The Bits Per Second(BPS) Unit Of Measurement Has Replaced It As A Better Expression Of Data Transmission Speed. Common Modem Speeds Are V.34 At 28.8 Kbps, V.34+ At 33.6 Kbps And V.90 At 56 Kbps.

    NETWORK INTERFACE CARD - A Network Interface Card, Often Abbreviated As NIC, Is An Expansion Board You Insert Into A Computer So The Computer Can Be Connected To A Network. Most Nics Are Designed For A Particular Type Of Network, Protocol And Media, Although Some Can Serve Multiple Networks.

    MEDIA CONVERTERS - Simple Networking Devices That Make It Possible To Connect Two Dissimilar Media Types Such As Twisted Pair With Fiber Optic Cabling. They Were Introduced To The Industry Nearly Two Decades Ago, And Are Important In Interconnecting Fiber Optic Cabling-Based Systems With Existing Copper-Based, Structured Cabling Systems.

    They Are Also Used In MAN Access And Data Transport Services To Enterprise Customers. Fiber Media Converters Support Many Different Data Communication Protocols Including Ethernet, Fast Ethernet, Gigabit Ethernet, T1/E1/J1, DS3/E3, As Well As Multiple Cabling Types Such As Coax, Twisted Pair, Multi-Mode And Single-Mode Fiber Optics. Media Converter Types Range From Small Standalone Devices And PC Card Converters To High Port-Density Chassis Systems That Offer Many Advanced Features For Network Management.

    SWITCHES AND NETWORKS - Switches Are A Fundamental Part Of Most Networks. Switches Enable Several Users To Send Information Over A Network. Users Can Send The Information At The Same Time And Do Not Slow Each Other Down. Just Like Routers Allow Different Networks To Communicate With Each Other, Switches Allow Different Nodes Of A Network To Communicate Directly With Each Other. A Node Is A Network Connection Point, Typically A Computer. Switches Allow The Nodes To Communicate In A Smooth And Efficient Manner.

    A Switch Is A Network Device That Filters And Forwards Packets Between LAN Segments And Ensures That Data Goes Straight From Its Origin To Its Proper Destination. Switches Remember The Address Of Every Node On The Network, And Anticipate Where Data Needs To Go.


  • Cut-Through .
  • Store And Forward .
  • Fragment-Free .

    CUT-THROUGH - Switches Read The MAC Address As Soon As A Packet Is Detected By The Switch. After Storing The Six Bytes That Make Up The Address Information, The Switches Immediately Begin To Send The Packet To The Destination Node, Even Though The Rest Of The Packet Is Coming Into The Switch.

    A SWITCH THAT USES STORE AND FORWARD - Saves The Entire Packet To The Buffer And Checks The Packet For Cyclic Redundancy Check (CRC) Errors Or Other Problems. If The Packet Has An Error, The Packet Is Discarded. Otherwise, The Switch Looks Up The MAC Address And Sends The Packet On To The Destination Node. Many Switches Combine The Two Methods By Using Cut-Through Until A Certain Error Level Is Reached, Then Changing Over To Store And Forward. Very Few Switches Are Strictly Cut-Through Because This Provides No Error Correction.

    A LESS COMMON METHOD IS FRAGMENT-FREE. Fragment-Free Works Like Cut-Through, But Stores The First 64 Bytes Of The Packet Before Sending The Packet On. The Reason For This Is That Most Errors And All Collisions Occur During The Initial 64 Bytes Of A Packet.


    SHARED-MEMORY—The Switch Stores All Incoming Packets In A Common Memory Buffer That All The Switch Ports (Input/Output Connections) Share. Then, The Switch Sends The Packets Out The Correct Port For The Destination Node.

    MATRIX—This Type Of Switch Has An Internal Grid With Which The Input Ports And The Output Ports Cross Each Other. When The Switch Detects A Packet On An Input Port, The Switch Compares The MAC Address To The Lookup Table To Find The Appropriate Output Port. The Switch Then Makes A Connection On The Grid Where These Two Ports Intersect.

    BUS-ARCHITECTURE—Instead Of A Grid, An Internal Transmission Path (COMMON BUS) Is Shared By All The Ports Using Time Division Multiplex Access (TDMA). A Switch With This Configuration Dedicates A Memory Buffer To Each Port. There Is An Application-Specific Integrated Circuit (ASIC) To Control The Internal Bus Access.


    Most Ethernet LAN Switches Use Transparent Bridging To Create The Address Lookup Tables. Transparent Bridging Technology Allows A Switch To Learn Everything That The Switch Needs To Know About The Location Of Nodes On The Network Without The Need For The Network Administrator To Do Anything. Transparent Bridging Has Five Parts:

  • Learning.
  • Flooding.
  • Filtering.
  • Forwarding.
  • Aging.

    BRIDGE - Functions The Same As A Repeater, But Can Also Divide A Network In Order To Reduce Traffic Problems. A Bridge Can Also Connect Unlike Network Segments (Ie. Token Ring And Ethernet). Bridges Create Routing Tables Based On The Source Address. If The Bridge Can't Find The Source Address It Will Forward The Packets To All Segments.

    A Bridge Reads The Outermost Section Of Data On The Data Packet, To Tell Where The Message Is Going. It Reduces The Traffic On Other Network Segments, Since It Does Not Send All Packets. Bridges Can Be Programmed To Reject Packets From Particular Networks. Bridging Occurs At The Data Link Layer Of The OSI Model, Which Means The Bridge Cannot Read IP Addresses, But Only The Outermost Hardware Address Of The Packet. In Our Case The Bridge Can Read The Ethernet Data Which Gives The Hardware Address Of The Destination Address, Not The IP Address. Bridges Forward All Broadcast Messages. Only A Special Bridge Called A Translation Bridge Will Allow Two Networks Of Different Architectures To Be Connected. Bridges Do Not Normally Allow Connection Of Networks With Different Architectures. The Hardware Address Is Also Called The MAC (Media Access Control) Address.


  • TRANSPARENT BRIDGING - Only One Bridge Is Used. They Build A Table Of Addresses (Bridging Table) As They Receive Packets. If The Address Is Not In The Bridging Table, The Packet Is Forwarded To All Segments Other Than The One It Came From. This Type Of Bridge Is Used On Ethernet Networks.

  • SOURCE ROUTE BRIDGING - Bridging Address Tables Are Stored On Each PC On The Network . The Source Computer Provides Path Information Inside The Packet. This Is Used On Token Ring Networks.

    NETWORK ROUTER- Functioning At The Network Later Of The OSI Model, A Router Is Similar To A Switch, But It Can Also Connect Different Logical Networks Or Subnets And Enable Traffic That Is Destined For The Networks On The Other Side Of The Router To Pass Through. Routers Create Or Maintain A Table Of The Available Routes And Can Be Configured To Use Various Routing Protocols To Determine The Best Route For A Given Data Packet. Routers Can Connect Networks That Use Disimilar Protocols. Routers Also Typically Provide Improved Security Functions Over A Switch.

    Also A Router Is Used To Route Data Packets Between Two Networks. It Reads The Information In Each Packet To Tell Where It Is Going. If It Is Destined For An Immediate Network It Has Access To, It Will Strip The Outer Packet, Readdress The Packet To The Proper Ethernet Address, And Transmit It On That Network. If It Is Destined For Another Network And Must Be Sent To Another Router, It Will Re-Package The Outer Packet To Be Received By The Next Router And Send It To The Next Router. The Section On Routing Explains The Theory Behind This And How Routing Tables Are Used To Help Determine Packet Destinations. Routing Occurs At The Network Layer Of The OSI Model. They Can Connect Networks With Different Architectures Such As Token Ring And Ethernet. Although They Can Transform Information At The Data Link Level, Routers Cannot Transform Information From One Data Format Such As TCP/IP To Another Such As IPX/SPX. Routers Do Not Send Broadcast Packets Or Corrupted Packets. If The Routing Table Does Not Indicate The Proper Address Of A Packet, The Packet Is Discarded.

    BROUTER - There is a device called a BROUTER which will function similar to a bridge for network transport protocols that are not routable, and will function as a router for routable protocols. It functions at the network and data link layers of the OSI network model.

    FIREWALL - Either A Hardware Or Software Entity (Or A Combination Of Both) That Protects A Network By Stopping Network Traffic From Passing Through It. In Most Cases, A Firewall Is Placed On The Network To Allow All Internal Traffic To Leave The Network (Email To The Outside World, Web Access, Etc.), But Stop Unwanted Traffic From The Outside World From Entering The Internal Network. This Is Achieved By Granting And Denying Access To Resources Based On A Set Of Configurable Rules.

    DHCP SERVER - A Server That Is Responsible For Assiging Unique IP Address To The Computers On A Network. A DHCP Server Prevents The Assignment Of Duplicate IP Addresses To Clients And Reduces Administrative Effort In Network Configuration. A DHCP Server Is Actually More Of A Service That Is Found On Network Operating Systems Such As Windows 2002/2008 Server, Or On Network Devices Such As Routers.


    MULTILAYER SWITCH - A Multilayer Switch (MLS) Is A Computer Networking Device That Switches On OSI Layer 2 Like An Ordinary Network Switch And Provides Extra Functions On Higher OSI Layers. Some Mlss Are Also Able To Route Between VLAN And/Or Ports Like A Common Router. The Routing Is Normally As Quick As Switching (At Wirespeed). Some Switches Can Use Up To OSI Layer 7 Packet Information; They Are Called Layer 4-7 Switches, Content-Switches, Web-Switches Or Application-Switches.

    CONTENT SWITCH - The Main Function Of A Content Switch Is To Inspect The Network Data That It Receives So That It Can Decide Where On The Network That Data (Or Request) Needs To Be Forwarded To. Once This Is Determined The Data Is Sent To The Appropriate Server Which Can Handle The Data. In Most Cases The Switch Looks To See What Type Of Application Or Software The Request Is Targeted At. It Does This By Looking To See What Port The Requests Is Directed At.

    For Example: If The Data Is Targeted At An Ftp Port Then The Request Will Be Sent To An Ftp Sever. The Main Benefit Of This Approach Is That The Switch Acts As A Load Balancer As It Can Balance Data Or Requests Across The Different Type Of Application Servers Used By The Business. A Second Major Function That This Type Of Switch Can Perform Is To Look At The Incoming Requests And See Which Websites Are Targeted. This Is Important For Large Enterprises Or Hosting Companies. If For Example A Web Hosting Company Was Hosting Several Thousand Websites The Switch Could Direct Requests To The Specific Servers That The Websites Are Running On. These Devices Tend To Be Very Expensive.

    IDS/IPS - These Terms Stand For Intrusion Detection System And Intrusion Prevention System Respectively. IDS Is A Device (Or Application) That Monitors Network And/Or System Activities For Malicious Activities Or Policy Violations. IDS Is A Passive System That Gives Alerts When Something Suspicious Is Detected And Logs The Events Into A Database For Reporting. IPS, On The Other Hand, Sits Inline With Traffic Flows On A Network, Actively Shutting Down Attempted Attacks As They’re Sent Over The Wire. It Can Stop The Attack By Terminating The Network Connection Or User Session Originating The Attack, By Blocking Access To The Target From The User Account, IP Address, Or Other Attribute Associated With That Attacker, Or By Blocking All Access To The Targeted Host, Service, Or Application. Vendors Are Increasingly Combining The Two Technologies Into A Single Box, Now Referred To As IDPS. These Devices Are Used With, Not Instead Of, A Firewall.


    A Load Balancer Is A Hardware And/Or Software Solution That Provides Load Balancing Services. Load Balancing Is Used To Distribute Workloads Evenly Across Two Or More Computers, Network Links, Cpus, Hard Drives, Or Other Resources, In Order To Get Optimal Resource Utilization, Maximize Throughput, Minimize Response Time, And Avoid Overload. Using Multiple Components With Load Balancing, Instead Of A Single Component, May Increase Reliability Through Redundancy. As An Example, Google Receives Many, Many More Search Requests Than A Single Server Could Handle, So They Distribute The Requests Across A Massive Array Of Servers.

    MUTLIFUNCTION NETWORK DEVICES - As You Might Guess, Multifunction Network Devices Combine The Function Of Individual Devices Into A Single Unit. An Example Is Wireless Access Points Which Often Include One Or More Of The Following: Firewall, DHCP Server, Wireless Access Point, Switch, Gateway, And Router.

    DNS SERVER - DNS Is An Internet And Networking Service That Translates Domain Names Into IP Addresses. The Internet Is Based On Numerical IP Addresses, But We Use Domain Names Because They Are Easier To Remember. DNS Is The Service That Looks Up The IP Address For A Domain Name Allowing A Connection To Be Made. This Process Is Very Similar To Calling Information. You Call Them With A Name, They Check Their Database And Give You The Phone Number. The DNS Service Is Included With Server Operating Systems (Windows 2003/2008, Linux, Etc.) And Network Devices Such As Routers.

    BANDWIDTH SHAPER - Describes The Mechanisms Used To Control Bandwidth Usage On The Network. Bandwidth Shaping Is Typically Done Using Software Installed On A Network Server. From This Server, Administrators Can Control Who Uses Bandwidth, For What, And When. Bandwidth Shaping Establishes Priorities To Data Traveling To And From The Internet And Within The Network. A Bandwidth Shaper Essentially Performs Two Key Functions: Monitoring And Shaping.

    Monitoring Includes Identifying Where Bandwidth Usage Is High And At What Time Of Day. After That Information Is Obtained, Administrators Can Customize Or Shape Bandwidth Usage For The Best Needs Of The Network. I Am Unaware Why Comptia Listed This In The "Network Devices" Section Of Their Objectives, But Bandwidth Shapers Are Typically Software.

    PROXY SERVER - A Proxy Server Acts As A Middle-Man Between Clients And The Internet Providing Security, Administrative Control, And Caching Services. When A User Makes A Request For An Internet Service And It Passes Filtering Requirements, The Proxy Server Looks In Its Local Cache Of Previously Downloaded Web Pages. If The Item Is Found In Cache, The Proxy Server Forwards It To The Client. This Reduces Bandwidth Through The Gateway. If The Page Is Not In The Cache, The Proxy Server Will Request The Page From The Appropriate Server. Nowadays, The Functions Of Proxy Servers Are Often Built Into Firewalls.

    CSU/DSU - A Channel Service Unit/Data Service Unit (CSU/DSU) Acts As A Translator Between The LAN Data Format And The WAN Data Format. Such A Conversion Is Necessary Because The Technologies Used On WAN Links Are Different From Those Used On Lans. Although CSU/DSU's Look Similar To Modems, They Are Not Modems, And They Don't Modulate Or Demodulate Between Analog And Digital. All They Really Do Is Interface Between A 56K, T1, Or T3 Line And Serial Interface (Typically A V.35 Connector) That Connects To The Router. Many Newer Routers Have CSU/Dsus Built Into Them.


    POE - Generally Speaking, Power Over Ethernet Technology Describes A System To Safely Pass Electrical Power, Along With Data, On Ethernet Cabling. Standard Versions Of Poe Specify Category 5 Cable Or Higher. Power Can Come From A Power Supply Within A Poe-Enabled Networking Device Such As An Ethernet Switch Or From A Device Built For "Injecting" Power Onto The Ethernet Cabling. IP Phones, LAN Access Points, And Wifi Switches To RFID Readers And Network Security Cameras. All Of These Require More Power Than USB Offers And Very Often Must Be Powered Over Longer Runs Of Cable Than USB Permits. In Addition, Poe Uses Only One Type Of Connector, An 8P8C (RJ45), Whereas There Are Four Different Types Of USB Connectors.

    SPANNING TREE PROTOCOL - Prevents Looping Where There Exists More Than One Path Between Segments

    Spanning Tree Is One Of Three Bridging Methods A Network Administrator Can Use. Which Method You Use Usually Will Be Determined By The Network’s Size. The Simplest Method Is Transparent Bridging, Where Only One Bridge Or Switch Exists On The Network. The Next Is Source-Route, In Which Bridging Address Tables Are Stored On Each PC On The Network. Then There’s What You Came For, Spanning Tree, Which Prevents Loops Where There Exists More Than One Path Between Segments. STP Was Upgraded To Rapid Spanning Tree Protocol (RSTP).

    VLAN - A Broadcast Domain Is Normally Created By The Router. With VLAN’s, A Switch Can Create The Broadcast Domain. This Allows A Virtual Network, Independent Of Physical Location To Be Created.

    Is A Group Of Hosts With A Common Set Of Requirements That Communicate As If They Were Attached To The Same Broadcast Domain, Regardless Of Their Physical Location. A VLAN Has The Same Attributes As A Physical Local Area Network (LAN), But It Allows For End Stations To Be Grouped Together Even If They Are Not Located On The Same Network Switch. LAN Membership Can Be Configured Through Software Instead Of Physically Relocating Devices Or Connections.

    To Physically Replicate The Functions Of A VLAN, It Would Be Necessary To Install A Separate, Parallel Collection Of Network Cables And Equipment Which Are Kept Separate From The Primary Network. However Unlike A Physically Separate Network, Vlans Must Share Bandwidth; Two Separate One-Gigabit Vlans Using A Single One-Gigabit Interconnection Can Suffer Both Reduced Throughput And Congestion. It Virtualizes VLAN Behaviors (Configuring Switch Ports, Tagging Frames When Entering VLAN, Lookup MAC Table To Switch/Flood Frames To Trunk Links, And Untagging When Exit From VLAN.)

    TRUNKING - Vlans Are Local To Each Switch's Database, And VLAN Information Is Not Passed Between Switches. Trunk Links Provide VLAN Identification For Frames Traveling Between Switches. The VLAN Trunking Protocol (VTP) Is The Protocol That Switches Use To Communicate Among Themselves About VLAN Configuration.

    A Trunk Is A Line Or Link Designed To Handle Many Signals Simultaneously, And That Connects Major Switching Centers Or Nodes In A Communications System. The Transmitted Data Can Be Voice (As In The Conventional Telephone System) Data, Computer Programs, Images, Video Or Control Signals.

    Trunks Are Used To Interconnect Switches To Form Networks, And To Interconnect Local Area Networks (Lans) To Form Wide Area Networks (WAN S) Or Virtual Lans (Vlans). A Trunk Often Consists Of Multiple Wires, Cables, Or Fiber Optic Strands To Maximize The Available Bandwidth And The Number Of Channels That Can Be Accommodated. A Trunk Can Also Be A Broadband Wireless Link. The Use And Management Of Trunks In A Communications System Is Known As Trunking. It Minimizes The Number Of Physical Signal Paths, And Thus The Total Amount Of Cable Hardware, Required To Serve A Given Number Of Subscribers In A Network.

    In Cisco Networks, Trunking Is A Special Function That Can Be Assigned To A Port, Making That Port Capable Of Carrying Traffic For Any Or All Of The Vlans Accessible By A Particular Switch. Such A Port Is Called A Trunk Port, In Contrast To An Access Port, Which Carries Traffic Only To And From The Specific VLAN Assigned To It. A Trunk Port Marks Frames With Special Identifying Tags (Either ISL Tags Or 802.1Q Tags) As They Pass Between Switches, So Each Frame Can Be Routed To Its Intended VLAN. An Access Port Does Not Provide Such Tags, Because The VLAN For It Is Pre-Assigned, And Identifying Markers Are Therefore Unnecessary.

    PORT MIRRORING - Used On A Network Switch To Send A Copy Of Network Packets Seen On One Switch Port (Or An Entire VLAN) To A Network Monitoring Connection On Another Switch Port. This Is Commonly Used For Network Appliances That Require Monitoring Of Network Traffic, Such As An Intrusion-Detection System.

    PORT AUTHENTICATION - The IEEE 802.1x Standard Defines 802.1x Port-Based Authentication As A Client-Server Based Access Control And Authentication Protocol That Restricts Unauthorized Clients From Connecting To A LAN Through Publicly Accessible Ports. The Authentication Server Validates Each Client Connected To A Switch Port Before Making Available Any Services Offered By The Switch Or The LAN.


    INSTALL CLIENT – The Actual Steps Taken To Set Up A Computer, Laptop Or Other Network Connected Device To The Network. This May Be In The Form Of Just Getting It Correctly Configured To Use TCP/IP Or More Involved Such As Installing A Software Suite So That Specific Network Parameters Can Be Leveraged For Proper Connectivity To Network Resources Or Resources On The Domain.

    NETWORK CONNECTIONS DIALOG BOX – Used To Configure Different Aspects Of The Network Connections By Way Of A Graphical User Interface (GUI) Within The Microsoft Windows Operating Systems. With Respect To Peer To Peer Networks, You Can Use The Network Tasks Pane To Create A New Connection, Set Up A Home Or Small Office Network As Well As Change The Windows Firewall Settings And View Available Wireless Networks.

    WIRELESS NETWORK CONNECTION DIALOG BOX – The Graphical User Interface (GUI) Within The Microsoft Windows Operating Systems Used To Configure The Wireless Devices And Their Settings. On The General Tab You Can Configure The Specific Hardware Settings (Parameters, Drivers, Etc) As Well As The Protocols (E.G. TCP/IP) And The Network Client That The Device Will Use (E.G. Client For Microsoft Networks). Additionally, You Can Install Services From This Screen As Well (E.G. Virtual Machine Network Service). The Wireless Networks Tab Will Show You The Available Networks And Allow You To Configure Preference For Each Of The Networks Encountered.

    ACCESS POINT PLACEMENT – Correctly Positioning Your Wireless Access Points Will Allow For The Seamless Use Of Wireless Devices On Your Network. By Correctly Placing The Devices, Users Will Not Generally Experience Signal Loss Of Their Connection To The Network. It Is Important To Understand That There Are Many Things That Affect The Wireless Access Point Signal With Respect To Broadcast And Receiving Strength That Include The Construction And Architecture Of The Building Where The Devices Are Distributed As Well As General Disruption Of The Frequency Range That The Access Points Operate On By Other Devices (E.G. Microwave Ovens, Cordless Phones, Etc).

    PHYSICAL LOCATIONS OF WIRELESS ACCESS POINTS (WAPS) – Device Placement Best Practices Include Planning For More Than Just Nominal Half Distances Between Devices. Consideration Needs To Be Given To What Type Of Obstructions May Be Currently In The Way (Physical Fire Breaks In Between Walls; Metal Superstructure, Etc) As Well As Future Plans To Subdivide Offices. Electrical Motors And Other Higher Current Carrying Lines Need To Be Considered As Well To Keep Interference To A Minimum.

    WIRED OR WIRELESS CONNECTIVITY – Planning For WAP To WAP Connections Only Or A Mix Of Wired And Wireless Connections. It’s Easier To Connect WAP To WAP In A Daisy Chain Signal Relay Configuration But When You Do This You Need To Realize That A Physical Failure In One WAP Device May Take Out All The Devices. It Is More Work And It Costs More In Time Money And Effort To Connect The Waps Using Wired Connections Back To A Switch Or A Router But It Greatly Reduces The Potential Connectively Loss On The Network; The Loss Of A Single WAP Where The Waps Are Wired Back Results In Only Impacting The Users Of That One WAP Instead Of All Waps Up And Downstream.

    INSTALL ACCESS POINT – Another Term For The Wireless Access Point(S) That Will Allow You To Correctly Gain Access To The Network With Your Device. This Point Onto The Network Will Allow The Client Device To Configure Itself With The Necessary Encryption (If Required) And Any Other Network Required Settings Or Else Risk Being Defaulted Off The Network.

    CONFIGURING ENCRYPTION – With Respect To Wireless Clients These Are The Settings Most Commonly Used. Disabled Simply Means That Everything Is Passed As Clear Text. Wired Equivalent Privacy (WEP) Is The Lowest Form Of The Types Of Encryption Available And Is Generally Only Used Today To Allow Legacy Devices That Cannot Handle More Robust Encryption Protocols To Gain Somewhat Secured Access To The Network. WEP Has Been Challenged And Defeated For A Number Of Years Mainly Due To The Increase In Computing Power And The Fact That The Keys Are Alphanumeric Or Hexadecimal Characters That Are Configured In 40 Bit, 64 Bit, 128 Bit, 153 Bit And 256 Bit Strength.

    WI-FI Protected Access (WPA) Was Created By The Wi-Fi Alliance To Better Secure Wireless Networks And Was Created In Response To The Weaknesses Researchers Found In Wired Equivalent Privacy (WEP). Temporal Key Integrity Protocol (TKIP) Is Used In WPA To Encrypt The Authentication And Encryption Information That Was Initially Passed On The Wire In Clear Text Before A Network Node Could Secure Its Communications On The Network. Wi Fi Protected Access Version 2 (WPA2) Offers Additional Protection Because It Uses The Strongest Authentication And Encryption Algorithms Available In The Advanced Encryption Standard (AES).

    CONFIGURING CHANNELS AND FREQUENCIES – Most Wireless Routers Work In The 2.4ghz Frequency Range And Require Network Administrators To Set Up The Channels For The Devices To Use. 1, 6 And 11 Are The Main Channels Used Because They Generally Will Not Be Interfered With From Other Devices Such As Cordless Phones And Bluetooth Devices That Also Work At This Frequency Range.

    SETTING ESSID AND BEACON – Extended Service Set Identifier (ESSID) Is The “Advertisement” From The Wireless Access Point That Basically Announces Its Availability For Network Devices To Make A Connection. The Announcement Signal That Is Sent Out Is Called The Beacon.

    VERIFYING INSTALLATION - The Process That Is Outlined For Making Sure That All The Settings Needed To Connect A Network Node To The Wireless Device. The Best Practice Steps Generally Include On Initial Installation Of The Wireless Access Point (WAP) To Do So Without Any Security To Verify That A Client Can Get On The Network. Once That Is Successful You Would Then Incorporate The Security Protocol That You Wanted To Use And To Make Sure The Client Can Operate On The Network Again. Once This Is Successfully Done It Is Assumed All Other Network Nodes Would Be Able To Successfully Repeat The Same Steps To Access The Network Securely And With The Traffic Encrypted.


    The OSI Networking Model Is Divided Into 7 Layers. Each Layer Has A Different Responsibility, And All The Layers Work Together To Provide Network Data Communication.


    APPLICATION: Represents User Applications, Such As Software For File Transfers, Database Access, And E-Mail. It Handles General Network Access, Flow Control, And Error Recovery. Provides A Consistent Neutral Interface For Software To Access The Network And Advertises The Computers Resources To The Network.

    PRESENTATION: Determines Data Exchange Formats And Translates Specific Files From The Application Layer Format Into A Commonly Recognized Data Format. It Provides Protocol Conversion, Data Translation, Encryption, Character-Set Conversion, And Graphics-Command Expansion.

    SESSION: Handles Security And Name Recognition To Enable Two Applications On Different Computers To Communicate Over The Network. Manages Dialogs Between Computers By Using Simplex(Rare), Half-Duplex Or Full-Duplex. The Phases Involved In A Session Dialog Are As Follows: Establishment, Data-Transfer And Termination.

    TRANSPORT: Provides Flow Control, Error Handling, And Is Involved In Correction Of Transmission/Reception Problems. It Also Breaks Up Large Data Files Into Smaller Packets, Combines Small Packets Into Larger Ones For Transmission, And Reassembles Incoming Packets Into The Original Sequence.

    NETWORK: Addresses Messages And Translates Logical Addresses And Names Into Physical Addresses. It Also Manages Data Traffic And Congestion Involved In Packet Switching And Routing. It Enables The Option Of Specifying A Service Address (Sockets, Ports) To Point The Data To The Correct Program On The Destination Computer.

    DATA LINK: The Interface Between The Upper "Software" Layers And The Lower "Hardware" Physical Layer. One Of Its Main Tasks Is To Create And Interpret Different Frame Types Based On The Network Type In Use.


    The Media Access Control (MAC) Sub-Layer And The Logical Link Control (LLC) Sub-Layer.

  • LLC SUB-LAYER Starts Maintains Connections Between Devices (E.G. Server - Workstation).

  • MAC SUB-LAYER Enables Multiple Devices To Share The Same Medium. MAC Sub-Layer Maintains Physical Device (MAC) Addresses For Communicating Locally (The MAC Address Of The Nearest Router Is Used To Send Information Onto A WAN).

    PHYSICAL: The Specification For The Hardware Connection, The Electronics, Logic Circuitry, And Wiring That Transmit The Actual Signal. It Is Only Concerned With Moving Bits Of Data On And Off The Network Medium. Most Network Problems Occur At The Physical Layer.

    Here Is An Idiotic, Yet Easy Way To Remember The 7 Layers. Memorize The Following Sentence: All People Seem To Need Data Processing. The First Letter Of Each Word Corresponds To The First Letter Of The Layers Starting With Application And Ending With The Physical Layer.

    QUALITY OF SERVICE (QoS) - Is A Set Of Parameters That Controls The Level Of Quality Provided To Different Types Of Network Traffic. Qos Parameters Include The Maximum Amount Of Delay, Signal Loss, Noise That Can Be Accommodated For A Particular Type Of Network Traffic, Bandwidth Priority, And CPU Usage For A Specific Stream Of Data. These Parameters Are Usually Agreed Upon By The Transmitter And The Receiver. Both The Transmitter And The Receiver Enter Into An Agreement Known As The Service Level Agreement (SLA). In Addition To Defining Qos Parameters, The SLA Also Describes Remedial Measures Or Penalties To Be Incurred In The Event That The ISP Fails To Provide The Qos Promised In The SLA.


    Time-To-Live (TTL) Is A Value In An Internet Protocol (IP) Packet That Tells A Network Router Whether Or Not The Packet Has Been In The Network Too Long And Should Be Discarded. For A Number Of Reasons, Packets May Not Get Delivered To Their Destination In A Reasonable Length Of Time.

    For Example, A Combination Of Incorrect Routing Tables Could Cause A Packet To Loop Endlessly. A Solution Is To Discard The Packet After A Certain Time And Send A Message To The Originator, Who Can Decide Whether To Resend The Packet.

    The Initial TTL Value Is Set, Usually By A System Default, In An 8-Binary Digit Field Of The Packet Header. The Original Idea Of TTL Was That It Would Specify A Certain Time Span In Seconds That, When Exhausted, Would Cause The Packet To Be Discarded.

    Since Each Router Is Required To Subtract At Least One Count From The TTL Field, The Count Is Usually Used To Mean The Number Of Router Hops The Packet Is Allowed Before It Must Be Discarded. Each Router That Receives A Packet Subtracts One From The Count In The TTL Field. When The Count Reaches Zero, The Router Detecting It Discards The Packet And Sends An Internet Control Message Protocol (ICMP) Message Back To The Originating Host.

    The Default Windows 95/98 TTL Value Is 32 Hops. Some Users Recommend Changing This To 128 If You Have Difficulty Reaching Certain Sites.

    The Ping And The Traceroute Utilities Both Make Use Of The TTL Value To Attempt To Reach A Given Host Computer Or To Trace A Route To That Host. Traceroute Intentionally Sends A Packet With A Low TTL Value So That It Will Be Discarded By Each Successive Router In The Destination Path. The Time Between Sending The Packet And Receiving Back The ICMP Message That It Was Discarded Is Used To Calculate Each Successive Hop Travel Time.

    Using The Multicast IP Protocol, The TTL Value Indicates The Scope Or Range In Which A Packet May Be Forwarded. By Convention:

  • 0 Is Restricted To The Same Host.
  • 1 Is Restricted To The Same Subnet.
  • 32 Is Restricted To The Same Site.
  • 64 Is Restricted To The Same Region.
  • 128 Is Restricted To The Same Continent.
  • 255 Is Unrestricted.

    WHAT IS TTL OR TIME TO LIVE? TTL, Or Time-To-Live, Is The Length Of Time For When A Zone File Is Set To Expire. This Is Usually Expressed In Number Of Seconds.

    If You Ask Your Local DNS Server (Usually Provided By Your ISP) For An Internet Address, The Server Will Figure Out Where To Find An Authoritative Answer. Once Provided The Answer, It Will Keep The Answer In A Local Cache So That If You, Or Someone Else, Ask For The Same Address Again It Will Not Need To Make The Request Again.

    When Domain Administrators Configure Their DNS Records, They Decide How Long The Records Should Remain In Remote Caches. Typically, A Remote Server Will Only Cache Those Records For The Length Of Time Specified By The TTL. After That, The Remote Server Will Remove The Zone File From Its Local Cache And Ask Again For An Authoritative Answer. Due To This, Shorter Ttls Can Cause Heavier Loads On An Authoritative Nameserver.


    The Default TTL Is 42300, Or 12 Hours.


    If You Lower The TTL It Will Set To 300, Or 5 Minutes.


    When You Lower The TTL To 300, Or 5 Minutes, It Will Take Effect On (Mt) Media Temple's Servers Immediately. But For The TTL To Propagate Across The Internet You Will Need To Wait From 12 To 48 Hours. It Is Best To Lower Your TTL 2 Days Before You Plan On Changing Your DNS So The Change Will Propagate Across The Internet In The Fastest Possible Way.


    If You Require A Custom TTL Value, Please Submit A Support Request Along With The Requested TTL Value, And Why It Is Required.


    The Following Are A Few Examples Of When Lowering The Ttl Would Be Useful.

  • Transferring A Domain Between Hosts.
  • Transferring A Domain Between Accounts Or Servers.
  • When Changing An IP Address For A Domain.
  • When Changing The MX Records Or DNS Records For A Domain.


    1. Login to your AccountCenter.
    2. Click on the domain for which you wish to lower your TTL.
    3. Click on Edit Zone File.
    4. Click on Lower TTL Value,

    TTL IS USED WHEN A "PING," Or A Request For A Response, Is Sent To Another Computer, The TTL Represents The Number Of Hops, Or Servers In Different Locations, The Request Can Travel To Before Returning A Failed Attempt Message.

    The Ping And... The Traceroute Utilities Both Make Use Of The TTL Value To Attempt To Reach A Given Host Computer Or To Trace A Route To That Host. Traceroute Intentionally Sends A Packet With A Low TTL Value So That It Will Be Discarded By Each Successive Router In The Destination Path. The Time Between Sending The Packet And Receiving Back The ICMP Message That It Was Discarded Is Used To Calculate Each Successive Hop Travel Time.

    Each Router That The Packet Travels Through Is Required To Subtract At Least One Count From The TTL Field.

    If The Time-To-Live Is Reduced To Zero (Or Less), The Packet MUST Be Discarded.The Time-To-Live Is Sometimes Used As A Hop Count Limit And Other Times As A Time Limit.Each Router That Handles A Packet MUST Decrement The TTL By At Least One, Even If The Elapsed Time Was Much Less Than A Second. Time-To-Live Functions As A Hop Count In This Perspective.

    When A Router Forwards A Packet, It MUST Reduce The TTL By At Least One. If It Holds A Packet For More Than One Second, It MAY Decrement The TTL By One For Each Second. This Way, Time-To-Live Is Used As A Time Count.

    If A Packet's TTL Field Reached Zero, The Router Detecting It Discards The Packet And Sends An ICMP (Internet Control Message Protocol) Message Back To The Originating Host.

    The Time Between Sending A Packet And Receiving The ICMP Message That It Was Discarded Is Used To Calculate The Travel Time For Each Successive Hop.

    A Specific Ttl Number Can Indicate The Maximum Range For A Packet.

    LOAD BALANCING - Is A Technique To Distribute Workload Evenly Across Two Or More Computers, Network Links, Cpus, Hard Drives, Or Other Resources, In Order To Get Optimal Resource Utilization, Maximize Throughput, Minimize Response Time, And Avoid Overload. Using Multiple Components With Load Balancing, Instead Of A Single Component, May Increase Reliability Through Redundancy. The Load Balancing Service Is Usually Provided By A Dedicated Program Or Hardware Device (Such As A Multilayer Switch Or A DNS Server).

    FAULT-TOLERANCE - Describes A Computer System Or Component Designed So That, In The Event That A Component Fails, A Backup Component Or Procedure Can Immediately Take Its Place With No Loss Of Service. Fault Tolerance Can Be Provided With Software, Or Embedded In Hardware, Or Provided By Some Combination. In The Software Implementation, The Operating System Provides An Interface That Allows A Programmer To "Checkpoint" Critical Data At Pre-Determined Points Within A Transaction. In The Hardware Implementation (For Example, With Stratus And Its VOS Operating System), The Programmer Does Not Need To Be Aware Of The Fault-Tolerant Capabilities Of The Machine.

    At A Hardware Level, Fault Tolerance Is Achieved By Duplexing Each Hardware Component. Disks Are Mirrored. Multiple Processors Are "Lock-Stepped" Together And Their Outputs Are Compared For Correctness. When An Anomaly Occurs, The Faulty Component Is Determined And Taken Out Of Service, But The Machine Continues To Function As Usual.


    BANDWIDTH - Is The Average Number Of Bits That Can Be Transmitted From The Source To A Destination Over The Network In One Second.

    LATENCY - (AKA "LAG") Is The Amount Of Time It Takes A Packet Of Data To Move Across A Network Connection. When A Packet Is Being Sent, There Is "Latent" Time, When The Computer That Sent The Packet Waits For Confirmation That The Packet Has Been Received. Latency And Bandwidth Are The Two Factors That Determine Your Network Connection Speed. Latency In A Packet-Switched Network Is Measured Either One-Way (The Time From The Source Sending A Packet To The Destination Receiving It), Or Round-Trip (The One-Way Latency From Source To Destination Plus The One-Way Latency From The Destination Back To The Source). Round-Trip Latency Is More Often Quoted, Because It Can Be Measured From A Single Point. Note That Round Trip Latency Excludes The Amount Of Time That A Destination System Spends Processing The Packet. Many Software Platforms Provide A Service Called Ping That Can Be Used To Measure Round-Trip Latency. Ping Performs No Packet Processing; It Merely Sends A Response Back When It Receives A Packet (I.E. Performs A No-Op), Thus It Is A Relatively Accurate Way Of Measuring Latency.

    Where Precision Is Important, One-Way Latency For A Link Can Be More Strictly Defined As The Time From The Start Of Packet Transmission To The Start Of Packet Reception. The Time From The Start Of Packet Transmission To The End Of Packet Transmission At The Near End Is Measured Separately And Called Serialization Delay. This Definition Of Latency Depends On The Throughput Of The Link And The Size Of The Packet, And Is The Time Required By The System To Signal The Full Packet To The Wire.

    Some Applications, Protocols, And Processes Are Sensitive To The Time It Takes For Their Requests And Results To Be Transmitted Over The Network. This Is Known As Latency Sensitivity. Examples Of Latency Sensitive Applications Include VOIP, Video Conferencing, And Online Games. In A VOIP Deployment, High Latency Can Mean An Annoying And Counterproductive Delay Between A Speaker’s Words And The Listener’s Reception Of Those Words. Network Management Techniques Such As Qos, Load Balancing, Traffic Shaping, And Caching Can Be Used Individually Or Combined To Optimize The Network And Reduce Latency For Sensitive Applications. By Regularly Testing For Latency And Monitoring Those Devices That Are Susceptible To Latency Issues, You Can Provide A Higher Level Of Service To End Users.

    PACKET LOSS - Is The Failure Of One Or More Transmitted Packets To Arrive At Their Destination. This Event Can Cause Noticeable Effects In All Types Of Digital Communications.


  • In Text And Data, Packet Loss Produces Errors.
  • In Videoconference Environments It Can Create Jitter.
  • In Pure Audio Communications, Such As Voip, It Can Cause Jitter And Frequent Gaps In Received Speech.
  • In The Worst Cases, Packet Loss Can Cause Severe Mutilation Of Received Data, Broken-Up Images, Unintelligible Speech Or Even The Complete Absence Of A Received Signal.

    The Causes Of Packet Loss Include Inadequate Signal Strength At The Destination, Natural Or Human-Made Interference, Excessive System Noise, Hardware Failure, Software Corruption Or Overburdened Network Nodes. Often More Than One Of These Factors Is Involved. In A Case Where The Cause Cannot Be Remedied, Concealment May Be Used To Minimize The Effects Of Lost Packets.

    ECHO - Is When Portions Of The Transmission Are Repeated. Echoes Can Occur During Many Locations Along The Route. Splices And Improper Termination In The Network Can Cause A Transmission Packet To Reflect Back To The Source, Which Causes The Sound Of An Echo. To Correct For Echo, Network Technicians Can Introduce An Echo Canceller To The Network Design. This Will Cancel Out The Energy Being Reflected.

    HIGH BANDWIDTH APPLICATIONS - A High Bandwidth Application Is A Software Package Or Program That Tends To Require Large Amounts Of Bandwidth In Order To Fulfill A Request. As Demand For These Applications Continues To Increase, Bandwidth Issues Will Become More Frequent, Resulting In Degradation Of A Network System. One Way To Combat The Effects Of These Applications On A Network Is To Manage The Amount Of Bandwidth Allocated To Them. This Allows Users To Still Use The Applications Without Degrading The Qos Of Network Services.


  • Thin Clients.
  • Voice Over IP.
  • Real Time Video.
  • Multi-Media.


    Gather Information on the Problem.


  • External Customers Dialing Into A Call Center To Order Products, Obtain Customer Service, And So Forth.

  • Internal Agents Receiving Incoming Calls From A Call Queue Or Initiating Outbound Collection Calls To Customers.

  • Internal Users Using Administrative Phones To Call Employees In Other Company Locations Or PSTN Destinations, And Perform Basic Actions Such As Call Transfers And Dialing Into Conferences.

    As The Network Administrator, You Must Collect Sufficient Information From These Users To Allow You To Isolate The Problem. Detailed, Accurate Information Will Make This Task Easier. As You Turn Up Your Network, You May Consider Putting These Questions In An On-Line Form. A Form Will Encourage Users To Provide More Details About The Problem And Also Put Them Into The Habit Of Looking For Particular Error Messages And Indicators. Capturing The Information Electronically Will Also Permit You To Retrieve And Re-Examine This Information In The Future, Should The Problem Repeat Itself.


    Determine If The Problem Is Limited To One Workstation, Or Several Workstations, One Server, One Segment, Or The Entire Network. If Only One Person Is Experiencing A Certain Problem, The Problem Is Most Likely At The Workstation. If Groups Of Workstations Are Affected, The Problem Might Lie At A Part Of The Network That Users All Have In Common, Such As A Particular Software Application Or Database, A Server, The Network Segment, Or The Network Configuration.


    Cisco Discovery Protocol (CDP) Cisco Proprietary Protocol That Is Media- And Protocol-Independent And Runs On All Cisco Manufactured Equipment Over Any Layer-2 Protocol That Supports Subnetwork Access Protocol (SNAP) Frames Including Ethernet, Frame Relay, And ATM. With CDP, Network Management Applications Can Obtain The Device Type And The SNMP IP Address Of Neighboring Devices.

    CDP Allows Network Management Applications To Dynamically Discover Cisco Devices That Are Neighbors Of Already Known Devices, Neighbors Running Lower-Layer Transparent Protocols In Particular. CDP Runs Over The Data Link Layer Only, Not The Network Layer. Therefore, Two Systems That Support Different Network Layer Protocols Can Learn About Each Other. Cached CDP Information Is Available To Network Management Applications. However, Cisco Devices Never Forward A CDP Packet. When New Information Is Received, Old Information Is Discarded.

    CDP Is Enabled By Default But You Can Use The No Cdp Run Global Command To Disable CDP. You Can Also Disable CDP Per Interface By Using The No Cdp Enable Interface Command. In Catalyst OS (Catos), The Command To Globally Disable CDP Is Set Cdp Disable. In Catos, To Disable CDP On A Port, Use The Set Cdp Disable [Mod/Port] Command.

    To Find Out About Neighboring Cisco Routers Or Switches, Use The Show Cdp Neighbors Command, Which Gives Summary Information Of Each Router. You Use The Same Command On A Catalyst Switch. To Get More Detailed Information About Neighboring Routers, Use The Show Cdp Neighbors Detail Command. From The Output, You Can Gather Neighbor Information Such As Name, IP Address, Platform Type, And IOS Version.

    PORT MIRRORING - Used On A Network Switch To Send A Copy Of Network Packets Seen On One Switch Port (Or An Entire Vlan) To A Network Monitoring Connection On Another Switch Port. This Is Commonly Used For Network Appliances That Require Monitoring Of Network Traffic, Such As An Intrusion-Detection System.

    Port Mirroring Is A Process Of Monitoring Network Traffic. Port Mirroring Monitors Network Traffic By Sending Copies Of All Incoming And Outgoing Packets From One Port To A Monitoring Port. These fast packets go from one port of a network switch to another port. It Is Used On A Network Switch To Send A Copy Of Network Packets Seen On One Switch Port (OR AN ENTIRE VLAN) To A Network Monitoring Connection On Another Switch Port.

    This Is Commonly Used For Network Appliances That Require Monitoring Of Network Traffic, Such As An Intrusion-Detection System.


    In Many Ways, Fiber-Optic Media Addresses The Shortcomings Associated With Copper-Based Media. Because Fiber-Based Media Use Light Transmissions Instead Of Electronic Pulses, Threats Such As EMI, Crosstalk, And Attenuation Become A Nonissue. Fiber Is Well Suited For The Transfer Of Data, Video, And Voice Transmissions. In Addition, Fiber-Optic Is The Most Secure Of All Cable Media. Anyone Trying To Access Data Signals On A Fiber-Optic Cable Must Physically Tap Into The Media. Given The Composition Of The Cable, This Is A Particularly Difficult Task.

    Unfortunately, Despite The Advantages Of Fiber-Based Media Over Copper, It Still Does Not Enjoy The Popularity Of Twisted-Pair Cabling. The Moderately Difficult Installation And Maintenance Procedures Of Fiber Often Require Skilled Technicians With Specialized Tools. Furthermore, The Cost Of A Fiber-Based Solution Limits The Number Of Organizations That Can Afford To Implement It. Another Sometimes Hidden Drawback Of Implementing A Fiber Solution Is The Cost Of Retrofitting Existing Network Equipment. Fiber Is Incompatible With Most Electronic Network Equipment. This Means That You Have To Purchase Fiber-Compatible Network Hardware.

    Fiber-Optic Cable Itself Is Composed Of A Core Glass Fiber Surrounded By Cladding. An Insulated Covering Then Surrounds Both Of These Within An Outer Protective Sheath. Figure 3 Shows The Composition Of A Fiber-Optic Cable.

    Two Types Of Fiber-Optic Cable Are Available: Single And Multimode Fiber. In Multimode Fiber, Many Beams Of Light Travel Through The Cable Bouncing Off Of The Cable Walls. This Strategy Actually Weakens The Signal, Reducing The Length And Speed The Data Signal Can Travel. Single-Mode Fiber Uses A Single Direct Beam Of Light, Thus Allowing For Greater Distances And Increased Transfer Speeds.

    Some Of The Common Types Of Fiber-Optic Cable Include The Following:

  • 62.5 Micron Core/125 Micron Cladding Multimode.
  • 50 Micron Core/125 Micron Cladding Multimode.
  • 8.3 Micron Core/125 Micron Cladding Single Mode.

    In The Ever-Increasing Search For Bandwidth That Will Keep Pace With The Demands Of Modern Applications, Fiber-Optic Cables Are Sure To Play A Key Rol.



    SPEED: Fiber Optic Networks Operate At High Speeds - Up Into The Gigabits

    BANDWIDTH: Large Carrying Capacity

    Distance: Signals Can Be Transmitted Further Without Needing To Be "Refreshed" Or Strengthened.

    RESISTANCE: Greater Resistance To Electromagnetic Noise Such As Radios, Motors Or Other Nearby Cables.

    MAINTENANCE: Fiber Optic Cables Costs Much Less To Maintain.

    In Recent Years It Has Become Apparent That Fiber-Optics Are Steadily Replacing Copper Wire As An Appropriate Means Of Communication Signal Transmission. They Span The Long Distances Between Local Phone Systems As Well As Providing The Backbone For Many Network Systems. Other System Users Include Cable Television Services, University Campuses, Office Buildings, Industrial Plants, And Electric Utility Companies.

    A Fiber-Optic System Is Similar To The Copper Wire System That Fiber-Optics Is Replacing. The Difference Is That Fiber-Optics Use Light Pulses To Transmit Information Down Fiber Lines Instead Of Using Electronic Pulses To Transmit Information Down Copper Lines. Looking At The Components In A Fiber-Optic Chain Will Give A Better Understanding Of How The System Works In Conjunction With Wire Based Systems.

    At One End Of The System Is A Transmitter. This Is The Place Of Origin For Information Coming On To Fiber-Optic Lines. The Transmitter Accepts Coded Electronic Pulse Information Coming From Copper Wire. It Then Processes And Translates That Information Into Equivalently Coded Light Pulses. A Light-Emitting Diode (Led) Or An Injection-Laser Diode (Ild) Can Be Used For Generating The Light Pulses. Using A Lens, The Light Pulses Are Funneled Into The Fiber-Optic Medium Where They Travel Down The Cable. The Light (Near Infrared) Is Most Often 850nm For Shorter Distances And 1,300nm For Longer Distances On Multi-Mode Fiber And 1300nm For Single-Mode Fiber And 1,500nm Is Used For For Longer Distances.

    Think Of A Fiber Cable In Terms Of Very Long Cardboard Roll (From The Inside Roll Of Paper Towel) That Is Coated With A Mirror On The Inside. If You Shine A Flashlight In One End You Can See Light Come Out At The Far End - Even If It's Been Bent Around A Corner.

    Light Pulses Move Easily Down The Fiber-Optic Line Because Of A Principle Known As Total Internal Reflection. "This Principle Of Total Internal Reflection States That When The Angle Of Incidence Exceeds A Critical Value, Light Cannot Get Out Of The Glass; Instead, The Light Bounces Back In. When This Principle Is Applied To The Construction Of The Fiber-Optic Strand, It Is Possible To Transmit Information Down Fiber Lines In The Form Of Light Pulses. The Core Must A Very Clear And Pure Material For The Light Or In Most Cases Near Infrared Light (850nm, 1300nm And 1500nm). The Core Can Be Plastic (Used For Very Short Distances) But Most Are Made From Glass. Glass Optical Fibers Are Almost Always Made From Pure Silica, But Some Other Materials, Such As Fluorozirconate, Fluoroaluminate, And Chalcogenide Glasses, Are Used For Longer-Wavelength Infrared Applications.


    For More - >


    The Goal Of This Article Is To Give An Easy Way To Understand "Useful Networking Concepts For Every Beginours Who Are Going To Study Networking.

    Some Topics That You Might Want To Pursue On Your Own That We Did Not Cover In This Article Are Listed Here, Thank You And Best Of Luck.

    This Article Written Author By: Premakumar Thevathasan. CCNA, CCNP, CCIP, MCSE, MCSA, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+.


    This Document Carries No Explicit Or Implied Warranty. Nor Is There Any Guarantee That The Information Contained In This Document Is Accurate. Every Effort Has Been Made To Make All Articles As Complete And As Accurate As Possible.

    It Is Offered In The Hopes Of Helping Others, But You Use It At Your Own Risk. The Author Will Not Be Liable For Any Special, Incidental, Consequential Or Indirect Any Damages Due To Loss Of Data Or Any Other Reason That Occur As A Result Of Using This Document. But No Warranty Or Fitness Is Implied. The Information Provided Is On An "As Is" Basic. All Use Is Completely At Your Own Risk.

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    Anonymous said...

    Loopback adapters and crossover cables are useful tools for troubleshooting both DDS &
    T1 circuits. This document shows the necessary pinout for building them as well as the
    uses for each. A T1 circuit is a dedicated line that consists of 24 channels that can run at
    56Kbps or 64Kbps for a total of up to 1.544Mbps. A DDS circuit is a dedicated line that
    consists of only one channel that can run at either 56Kbps or 64Kbps. If you do not know
    what type of router you are using, consult the documentation for that router. If you do
    not know what kind of circuit you are working with, contact the phone company that is
    providing it.

    Alex said...

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    you are my inspiration .your blog helps to understand various topics in easy manner

    Thank you

    THARU said...

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