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CISCO - DIFFERENCE IN BETWEEN ROUTER, SWITCH (LAYER 2 & LAYER 3), BRIDGE AND HUB: After Reading This Article, You’ll Understand The Difference In Between a Switch, A Router, And A Layer 3 Switches.



  • Application layer

  • Presentation layer

  • Session layer

  • Transportation layer

  • Network layer

  • Data-link layer

  • Physical layer

    For More About - > OSI 7 LAYERS :

    For More About - > OSI – TCP Vs UDP:

    SWITCHES Work At Layer 2 Of The OSI Model (Data-Link) And Switch Ethernet Frames Between Ethernet Devices.

    It Is A LAN Device That Can Also Be Called A Multi-Port Bridge. A Switch Switches Ethernet Frames Between Ethernet Devices. Switches Do Not Care About IP Addresses Nor Do They Even Examine IP Addresses As The Frames Flow Through The Switch. However, Unlike A Hub That Just Duplicates Data And Sends It Out All Ports, Switches Keep A Bridge Forwarding Table That Shows What MAC Addresses Have Been Seen On What Port.

    ROUTER : In General-Purpose Routers, Packet Switching Takes Place Using A Microprocessor.

    A Router, On The Other Hand, Works At Layer 3 Of The OSI Model (Network). It Is A WAN Device That Connects A LAN To A WAN Or A Subnetted LAN To Another Subnetted LAN. A Router Routes IP Packets Between IP Networks. Routers Do This Using An IP Routing Table. In That Table, They Have Either Static Or Dynamic Routes. When An IP Packet Comes In, The Router Looks Up The Destination IP In The IP Routing Table. If That Destination IP Is Not Found In The Table The Router Drops The Packet, Unless It Has A Default Route. Routers Form Broadcast Domains Because They Drop Broadcast Packets.



    Switches And Routers Have Been Separate And Distinct Devices. The Term Switch Was Reserved For Hardware-Based Platforms That Generally Functioned At Layer-2. For Example, Atm Switches Perform Hardware-Based Forwarding Of Fixed-Length Cells Whereas Ethernet Switches Use Mac Addresses To Make Forwarding Decisions. Conversely, The Term Router Has Been Used To Refer To A Device That Runs Routing Protocols To Discover The Layer-3 Topology And Makes Forwarding Decisions Based On Hierarchical Layer-3 Addresses. Because Of The Complexity Of These Tasks, Routers Have Traditionally Been Software-Based Devices. Routers Have Also Performed A Wide Variety Of "High Touch" And Value Added Features Such As Tunneling, Data-Link Switching (DLSW), Protocol Translation, Access Lists, And Dynamic Host Configuration Protocol (DHCP) Relay.

    A Router Is Similar In A Switch In That It Forwards Packets Based On Address. But, Instead Of The MAC Address That A Switch Uses, A Router Can Use The IP Address. This Allows The Network To Go Across Different Protocols.

    • Router Understand IP Head, And Switch Deal With MAC Address.

    • Router Has Its Own IP Address(Es), And Switch Don’t.

    • Router Has An Operating System Running Inside, And Allow Administrator To Login Into The System.

    • You (Network Administrator) Must Configure Routing Table To Make It Works.

    • Switch Is Usually Ready To Use.

    • Router Has Routing Software Running Inside, Including Route Discovery Protocol.

    • Routing Software Know How To Deal With Different IP Packet, Such As ICMP And Other IP Option Functionality. Switches Don’t.

    • Multiple Routers Can Be Connected Together As A Network.

    • You Can’t Directly Multiple Switches Together To Form A Large Network.



    Network Switches Operate At Layer 2 Of The OSI Model While Network Routers Operate At Layer 3. This Often Leads To Confusion Over The Definition Of "Layer 3 Switch."

    Layer 3 Switches Were Conceived As A Technology To Improve On The Performance Of Routers Used In Large Local Area Networks (LANS) Like Corporate Intranets. The Key Difference Between Layer 3 Switches And Routers Lies In The Hardware Technology Used To Build The Unit. The Hardware Inside A Layer 3 Switch Merges That Of Traditional Switches And Routers, Replacing Some Of A Router's Software Logic With Hardware To Offer Better Performance In Some Situations.

    Routers Were Devices That Connected The LAN To The WAN And Switches Were Just LAN Devices And You May Add A Layer 3 Switch To The LAN If You Had Some VLANS And Didn't Want To Use A Router.

    In General, A Layer-3 Switch (Routing Switch) Is Primarily A Switch (A Layer-2 Device) That Has Been Enhanced Or Taught Some Routing (Layer 3) Capabilities. A Router Is A Layer-3 Device That Simply Do Routing Only. In The Case Of A Switching Router, It Is Primarily A Router That Uses Switching Technology (High-Speed Asics) For Speed And Performance (As Well As Also Supporting Layer-2 Bridging Functions).

    The Idea Of Creating Layer-3 Switch Is Basically To Efficiently Do Inter-VLAN Routing Or To Do Internal Routing Between Multiple Broadcast Domains (Multiple LAN Where Each LAN Has Its Own Subnet) While Keeping Layer-2 Features Such As Spanning Tree And Trunking. However To Deal With "Border" Or "Edge" Of The Network And A Router Is Used Since A Router Is Basically Designed To Handle Traffic Across The Border Or The Edge Network.

    In A Layer 3 Switch Performs This Using Application Specific Integrated Circuit (ASIC) Hardware. Layer 3 Switch Is Really Like A High-Speed Router Without The WAN Connectivity.

    When It Comes To Layer 3 Switching, There Are Two Kinds: Hardware And Software. With A Hardware-Based Solution, The Device Is Using An ASIC (A Dedicated Chip) To Perform The Function. With The Software Implementation, The Device Is Using A Computer Processor And Software To Perform The Function. Generally, Layer 3 Switches And High-End Routers Route Packets Using Hardware (Asics) And General-Purpose Routers Use Software To Perform Routing Functions.

    The Layer 3 Switch Is There To Route Between Different Subnets Or VLANS On A Campus LAN Or Any Sort Of Large LAN. This Means That The Layer 3 Switch Is Really For Large Ethernet Networks That Need To Subnet Into Smaller Networks. Most Of The Time, This Is Done Using VLANS.

    • Routers Work At Layer 3 And Route IP Packets Between Networks.

    • For Some Of The Higher-End Cisco Switches, Enabling Layer 3 Switching Is Simply A Software Upgrade Available For A Fee.

    • Layer 3 Switches Are Used Primarily For Inter-VLAN Routing.

    • Layer 3 Switches Don’t Have WAN Connectivity

    • The Layer 3 Switch Looks Like A Switch. It Has 24+ Ethernet Ports And No WAN Interfaces.

    • The Layer 3 Switch Will Act Like A Switch When It Is Connecting Devices That Are On The Same Network.

    • The Layer 3 Switch Is The Same As A Switch With The Router’s IP Routing Intelligence Built In.

    • The Switch Works Very Quickly To Switch Or Route The Packets It Is Sent.

    Layer 3 Switches Often Cost Less Than Traditional Routers. Designed For Use Within Local Networks, A Layer 3 Switch Will Typically Not Possess The WAN Ports And Wide Area Network Features A Traditional Router Will Always Have.


    • Network With A Lot Of Broadcasts That Needs Better Performance.

    • Subnets And/Or VLANS That Are Currently Connected Via A Router.

    • Higher Performance VLANS.

    • Departments Need Their Own Broadcast Domains For Performance Or Security.

    • Considering Implementing VLANS.

    In General, You Want To Use A Router When Most Of The Time The Device Does Routing. Likewise, You Want To Use A Switch When When Most Of The Time The Device Does Switching. This Statement Becomes More Apparent When Dealing With Larger Network Like An ISP Or Large Corporation.

    Example In ISP Is That They Use Router (At Least 7600 Series) To Have Full View Of BGP (The Edge Router). As For Their "Internal Network", They Use Layer-3 Switches (Usually Catalyst 6500 Series).

    Cisco Catalyst Layer-3 Switches Are 3560, 3750, 4500 Series, 4900 Series, And 6500 Series. The Following Are Illustrations Of Layer-3 Switch With Examples Of Catalyst 3550 And 3560 Feature And Capabilities. Note That Catalyst 3550 Is Considered EOL And The Current Replacement Is The 3560.

    There Is Another Major Architectural Difference Between A Layer 3 Switch And A Router. A Traditional Router Organizes Bridging (Layer 2) And Routing (Layer 3) As Peers. A Layer 3 Switch Layers Routing On Top Of Switching, Permitting A More Natural Networking Architecture While Greatly Facilitating Scalability.

    Characteristic Layer 3 Switch Legacy Router
    Routes core LAN protocols: IP, IPX, AppleTalk Yes Yes
    Subnet definition Layer 2 switch domain Port
    Forwarding architecture Hardware Software
    RMON support Yes No
    Price Low High
    Forwarding performance High Low
    Policy performance High Low
    WAN support No Yes

    For More About - > CISCO - LAYER 3 SWITCHING :




    Network Switches And Bridges Are Both Layer 2 Devices. They Operate At The Data Link Layer (Layer 2) Of The OSI Reference Model. Network Switches And Bridges Have Many Similarities And Similar Function. But Switches Are Considered As Superior Devices Than Bridges, And Both Can Filter Data So That Only The Appropriate Segment Or Host Receives A Transmission.

    Both Filter Packets Based On The Physical Address (AKA MAC - Media Access Control - Address) Of The Sender/Receiver Although Newer Switches Sometimes Include The Capabilities Of A Router And Can Forward Data Based On IP Address (Operating At The Network Layer) And Are Referred To As IP Switches.

    In The Cisco World, The Bridge Forwarding Table Is Called A CAM Table, Or Content Addressable Memory Table. If A Switch Receives An Ethernet Frame For A Destination That It Doesn’t Have In Its Table, It Floods That Frame Out To All Ports (Like A Hub Does All The Time).

    However, The Switch Learns From The Response Of That Flood And Records The Response To That Frame In Its Forwarding Table For The Next Time. Switches Form Collision Domains. In Other Words, The Switches “Play Traffic Cop” With The Inbound Frames By Buffering Each Packet Before Switching It. This Way, There Are No Collisions And, To Each Device Connected To The Switch, It Seems Like That Device Has Its Own Ethernet Segment And Can Talk At Full Speed, Without Risk Of Collisions.

    Using Either A Switch Or A Bridge But *In General* Bridges Are Used To Extend The Distance Capabilities Of The Network While Minimizing Overall Traffic, And Switches Are Used To Primarily For Their Filtering Capabilities To Create Multiple, Smaller Virtual LAN's Out Of One Large LAN For Easier Management/Administration (V-LAN'S).


    • Packet Forwarding In Bridges Are Performed Using Software. Packet Forwarding In Switches Are Performed Using Asics (Application Specific Integrated Circuits).

    • Switches Operate Comparatively Higher Speeds That Bridges.

    • Method Of Switching Of A Bridge Is Store And Forward. Method Of Switching Of A Switch Can Be Store And Forward, Cut-Through Or Fragment-Free.

    • Normally A Switch Has More Ports Than A Bridge.

    • Bridges Can Operate Only In Half Duplex Mode, But A Switch Can Operate Both In Half Duplex Or Full Duplex Mode.

    • Both Bridge And Switch Has One Collision Domain Per Port, But Switches Have One Broadcast Domain Per VLAN.

    • Switchs Support Full-Duplex Local Area Network (LAN) Communication.



    Hubs Are Commonly Used To Connect Segments Of A LAN. A Hub Contains Multiple Ports. When A Packet Arrives At One Port, It Is Copied To The Other Ports So That All Segments Of The LAN Can See All Packets.

    In A Hub, A Frame Is Passed Along Or "Broadcast" To Every One Of Its Ports. It Doesn't Matter That The Frame Is Only Destined For One Port. The Hub Has No Way Of Distinguishing Which Port A Frame Should Be Sent To. Passing It Along To Every Port Ensures That It Will Reach Its Intended Destination. This Places A Lot Of Traffic On The Network And Can Lead To Poor Network Response Times.

    The Biggest Problem With Hubs Is Their Simplicity. Since Every Packet Is Sent Out To Every Computer On The Network, There Is A Lot Of Wasted Transmission. This Means That The Network Can Easily Become Bogged Down.

    Additionally, A 10/100Mbps Hub Must Share Its Bandwidth With Each And Every One Of Its Ports. So When Only One PC Is Broadcasting, It Will Have Access To The Maximum Available Bandwidth. If, However, Multiple Pcs Are Broadcasting, Then That Bandwidth Will Need To Be Divided Among All Of Those Systems, Which Will Degrade Performance.

    Switch: A Switch Steps Up On A Bridge In That It Has Multiple Ports. When A Packet Comes Through A Switch It Is Read To Determine Which Computer To Send The Data To. This Leads To Increased Efficiency In That Packets Are Not Going To Computers That Do Not Require Them.

    A Switch, However, Keeps A Record Of The MAC Addresses Of All The Devices Connected To It. With This Information, A Switch Can Identify Which System Is Sitting On Which Port. So When A Frame Is Received, It Knows Exactly Which Port To Send It To, Without Significantly Increasing Network Response Times. And, Unlike A Hub, A 10/100Mbps Switch Will Allocate A Full 10/100Mbps To Each Of Its Ports. So Regardless Of The Number Of Pcs Transmitting, Users Will Always Have Access To The Maximum Amount Of Bandwidth. It's For These Reasons Why A Switch Is Considered To Be A Much Better Choice Then A Hub.

    Router: A Router Is Similar In A Switch In That It Forwards Packets Based On Address. But, Instead Of The MAC Address That A Switch Uses, A Router Can Use The IP Address. This Allows The Network To Go Across Different Protocols.

    Routers Are Completely Different Devices. Where A Hub Or Switch Is Concerned With Transmitting Frames, A Router's Job, As Its Name Implies, Is To Route Packets To Other Networks Until That Packet Ultimately Reaches Its Destination. One Of The Key Features Of A Packet Is That It Not Only Contains Data, But The Destination Address Of Where It's Going.

    A Router Is Typically Connected To At Least Two Networks, Commonly Two Local Area Networks (Lans) Or Wide Area Networks (WAN) Or A LAN And Its ISP's Network .


    The Goal Of This Article Is To Give An Easy Way To Understand The “DIFFERENCE IN BETWEEN ROUTER, SWITCH (LAYER 2 & LAYER 3), BRIDGE AND HUB". Hope This Article Will Help Every Beginners Who Are Going To Start Cisco Lab Practice Without Any Doubts.

    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+.


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    Anonymous said...

    Most Switches Operate At The Data Layer (Layer 2) Of The OSI Reference Model, Some Incorporate Features Of A Router And Operate At The Network Layer (Layer 3) As Well. In Fact, A Layer 3 Switch Is Incredibly Similar To A Router.
    When A Router Receives A Packet, It Looks At The Layer 3 Source And Destination Addresses To Determine The Path The Packet Should Take. A Standard Switch Relies On The MAC Addresses To Determine The Source And Destination Of A Packet, Which Is Layer 2 (Data) Networking.
    The Fundamental Difference Between A Router And A Layer 3 Switch Is That Layer 3 Switches Have Optimized Hardware To Pass Data As Fast As Layer 2 Switches, Yet They Make Decisions On How To Transmit Traffic At Layer 3, Just Like A Router. Within The LAN Environment, A Layer 3 Switch Is Usually Faster Than A Router Because It Is Built On Switching Hardware. In Fact, Many Of Cisco's Layer 3 Switches Are Actually Routers That Operate Faster Because They Are Built On "Switching" Hardware With Customized Chips Inside The Box.
    The Pattern Matching And Caching On Layer 3 Switches Is Similar To The Pattern Matching And Caching On A Router. Both Use A Routing Protocol And Routing Table To Determine The Best Path. However, A Layer 3 Switch Has The Ability To Reprogram The Hardware Dynamically With The Current Layer 3 Routing Information. This Is What Allows For Faster Packet Processing.
    On Current Layer 3 Switches, The Information Received From The Routing Protocols Is Used To Update The Hardware Caching Tables.

    Anonymous said...


    To Represent The Traditional Inter-VLAN Routing Architectures. The Major Issue With These Architectures Is Performanceif Gigabit Speed Routing Is Required Between VLANS, Extremely High Performance And Costly Routers Are Required. A New Form Of Inter-VLAN Routing On The LAN Has Emerged In Recent Years Called Layer 3 Switching. With A Layer 3 Switch, The Traditionally Separated Layer 2 And Layer 3 Functions Are Combined Into A Single Device, Eliminating The Bottleneck Associated With The Cable Between A Router And Switch By Replacing The Cable With A High-Speed Backplane Connection. Layer 3 Switches Also Typically Perform Routing In Specially Designed Hardware Circuitry Rather Than Software, Using Specialized Hardware That Can Perform Routing Functions At High Speed. This Means That The Performance Of Layer 3 Switches Is Much Higher Than Traditional Router-On-A-Stick Architectures. For Example, If You Use A Cisco 3640 Series Router In The Router-On-A-Stick Architecture, You Can Achieve Routing Speeds Of Up To 40,000 Packets Per Second. If You Compare This With A Cisco Catalyst 3550-24-EMI Layer 3 Switch, Which Is Actually Cheaper Than A Cisco 3640 Router, You Can Route Packets At Up To 6.6 Million Packets Per Second. This Is Obviously Quite A Difference And Highlights The Limitations Of Using Router-On-A-Stick Architectures For Inter-VLAN Routing On The LAN. Of Course, The Cisco 3640 Router Still Has A Place In The Network; It Supports A Wide Variety Of Diverse Media, Including Serial And ATM Connections For WAN Connectivity; Also Supports Advanced Features Such As Firewalling, Encryption, And So ONALL Of Which Are Not Supported On Cisco Catalyst Switches.
    The Layer 3 Switch Uses Application-Specific Integrated Circuits (ASICS), Which Are Hardware Chips That Can Route Traffic At Very High Speeds. These Asics Are Installed On The Switching Engine Of A Layer 3 Switch, Which Traditionally Switches Frames At Layer 2. The Asics Allow The Switching Engine To Also Switch Frames That Contain Packets Sent Between Different VLANS. Each ASIC Is Programmed With The Information Required To Route Traffic From One VLAN To Another, Without Having To Pass The Traffic Through The CPU Of The Routing Engine. This Information Includes The Egress Port, Egress VLAN, And New Destination MAC Address That Should Be Written For The Frame That Is Sent. Some Form Of Route Cache Is Normally Used To Store Such Information, With The ASIC Searching The Cache For Routing Information For The Destination IP Address Of Packets As They Are Received. How This Information Is Programmed Into The Route Cache Depends On The Layer 3 Switch Architecture Used; However, The End Result Is Essentially The Same.
    In Addition To The High-Speed Routing Feature, These Asics Also Can Apply Security Access Control List (ACL) Filtering And Layer 3 Quality Of Service (QOS) Classification, All At Wire-Speed, Meaning These Useful Features Can Be Turned On Without Affecting Performance.