INTRODUCTION :
There Are Various Ways That Data Packets Can Be Moved Through A Network. Routing Is The General Term That Refers To The Way In Which Those Packets Are Moved Through A Network. Normally, Ways Which Define The Formats Of Packet Transfer In A Network Are Known As Routing Protocols.There Are Two Types Of Routing, Namely, Static And Dynamic. Static Routing Is Where Packets Move Through A Network With The Same Identical Path, All The Way To Their Destination. Static Routing Is Best Suited For Small Networks, While Dynamic Routing Is Better Suited On Larger Networks, For Instance, The Internet.
For Dynamic Routing, Packets Can Be Channeled To Another Path (Route) On The Fly By Routers, Given The Path Is Deemed A Better One Suited To Reach The Intended Destination. For Instance, If A Destination Can Be Reached Through Several Routes, Routers Will Normally Self-Configure To Route The Packets On The Shortest Path Available, Although, A Shorter Path Here Refers To One With Less Hops, As Opposed To Shorter In Distance. Routers Reprogram Their Routing Tables By ‘Communicating’ With Each Other Using Routing Protocols.
Although There Are Many Types Of Routing Protocols, Three Major Classes Are In Widespread Use On IP Networks :
◙ Interior Gateway Routing Via Link State Routing Protocols, Such As OSPF And IS-IS.
◙ Interior Gateway Routing Via Path Vector Or Distance Vector Protocols, Such As IGRP And EIGRP
◙ Exterior Gateway Routing. The Border Gateway Protocol (BGP) Is The Routing Protocol Used On The Internet For Exchanging Traffic Between Autonomous Systems.
And Also Most Known Protocols Is The Routing Information Protocol (RIP). Many Routing Protocols Are Defined In Documents Called RFCs
The Specific Characteristics Of Routing Protocols Include The Manner In Which They Avoid Routing Loops, The Manner In Which They Select Preferred Routes, Using Information About Hop Costs, The Time They Require To Reach Routing Convergence, Their Scalability, And Other Factors.
ROUTING PROTOCOL HAS TWO TYPES :
1. First One Is Interior Gate Way Protocol2. And Other One Is Exterior Gateway Protocol.
INTERIOR ROUTING PROTOCOLS :
Interior Gateway Protocols (IGPs) Exchange Routing Information Within A Single Routing Domain. Examples Of IGPs Include:◙ Open Shortest Path First (OSPF)
◙ Routing Information Protocol (RIP)
◙ Intermediate System To Intermediate System (IS-IS)
◙ EIGRP, Cisco's Proprietary Enhanced Interior Gateway Routing Protocol.
Cisco No Longer Supports IGRP, Another Proprietary Protocol. The EIGRP Implementation Accepts IGRP Configuration Commands, But The Internals Of IGRP And EIGRP Are Different.
WHY IS IGRP NO LONGER SUPPORTED ON THE NEW CISCO IOS?
EIGRP - Enhanced Interior Gateway Routing Protocol , IGRP - Interior Gateway Routing Protocol. IGRP And EIGRP Are Both Cisco Proprietary Routing Protocols).EIGRP (Enhanced IGRP) Has Replaced IGRP. With The Way EIGRP Is Set Up As A Protocol It Is Possible To Implement A Newer Router That Only Supports EIGRP Into A Network That Is Running IGRP. Honestly Network Admins Should Be Pushing For EIGRP If They Are Still On IGRP As For Many Features And Advantages EIGRP Has Over IGRP.
ROUTING PROTOCOLS VENDOR-DRIVEN :
General:◙ - ➤ BABEL.
◙ - ➤ B.A.T.M.A.N.
◙ - ➤ BGP.
◙ - ➤ IS-IS.
◙ - ➤ OLSR.
◙ - ➤ OSPF.
◙ - ➤ RIP.
Vendor-Driven:
(CISCO) - ➤ IGRP / EIGRP.
(NORTEL) - ➤ SMLT / R-SMLT / DSMLT.
Special-purpose :
◙ - ➤ CTP.
◙ - ➤ CSPF.
◙ - ➤ DVMRP.
Defunct:
◙ - ➤ BGMP.
◙ - ➤ EGP.
OSPF Is Also Interior Gate Way Protocol, Other Interior Gate Way Protocol Are RIP, EIGRP, IGRP. BGP And BGP4 Is Exterior Gate Way Protocol. The Dynamic Routing Protocols Keep The Routing Tables Updated.
This Articles Is Specification The Open Shortest Path First (OSPF), Enhanced Interior Gateway Routing Protocol (EIGRP) And Routing Information Protocol (RIP) TCP/IP Internet Routing. These Three Protocols Are Classier As Interior Gateway Protocol (IGP). The Network Based On TCP/IP Protocol Permits The Efficient Routing Of Data Packets Based On Their IP Address. Routers Are Used In The Network To Control And Forward Data.
In The Packetized Communication Of Information, The Function Of Routing Is Moving Traffic Across Networks And The Routers Should Be Aware Of Where They Should Forward The Traffic Next In Order To Reach The Final Destination. In Order For Routers To Effectively And Efficiently Distribute Data, The Choice Of The Routing Protocol Becomes Very Critical Factor To Define The Success Of The Network Over Time. Factors That Differentiate One Routing Protocol From Another Include The Speed That It Adapts To Topology Changes Called As Convergence, The Ability To Choose The Best Route Among Multiple Routes And The Amount Of Network Traffic That The Routing Protocol Creates.
ROUTED PROTOCOLS
Examples Of Routed Protocols Are: IP, IPX and Appletalk Are Three Common Routed Protocols.
A Routed Protocol Is - Used To Deliver Application Traffic. It Provides Appropriate Addressing Information In Its Internet Layer (Network Layer) Addressing To Allow A Packet To Be Forwarded From One Network To Another.
ROUTED PROTOCOLS INCLUDE :
◙ - ► Internet Protocol◙ Telnet
◙ Remote Procedure Call (RPC)
◙ SNMP
◙ SMTP
◙ - ► Novell IPX
◙ - ► Open Standards Institute Networking Protocol
◙ - ► DECnet
◙ - ► Appletalk
◙ - ► Banyan Vines
◙ - ► Xerox Network System (XNS)
ROUTING PROTOCOLS
ROUTING CHARACTERISTICS :
Packets Originating From A Nonrouting Device Destined For Another Network Are Sent To Their Default Gateway (Layer 3 Device On Segment). The Router Consults Its Routing Table To Determine If The Destination Network Can Be Reached. If Not, The ICMP Destination Unreachable Message Is Sent To The Source. If So, Packet Is Forwarded Out Interface Associated With The Destination Network In Routing Table.ROUTING SOURCES :
• Connected Interfaces: As Soon As We Assign An IP Address To A Working (Up/Line Protocol Up) Interface, The Router Associates The Entire Subnet Of The Interface’s IP Address In The Routing Table.• Static Routes: Manual Entries That An Administrator Enters Into The Configuration That Describe The Destination Network And The Next Hop (Router Along The Destination Path).
• Routing Protocols: Protocols Exchanged Between Routing Devices To Dynamically Advertise Networks.
A Routing Protocol Specifies How Routers Communicate With Each Other, Disseminating Information That Enables Them To Select Routes Between Any Two Nodes On A Computer Network. Routing Algorithms Determine The Specific Choice Of Route. Each Router Has A Priori Knowledge Only Of Networks Attached To It Directly. A Routing Protocol Shares This Information First Among Immediate Neighbors, And Then Throughout The Network. This Way, Routers Gain Knowledge Of The Topology Of The Network.
Routing Is The Process Of Moving Data From One Network To Another Network. Within A Network, All Hosts Are Directly Accessable And Do Not Need To Pass Data Through A Default Gateway. All Hosts On The Same Network Are Directly Connected And Can Communicate Directly With Each Other.
CLASSFUL ROUTING VS CLASSLESS ROUTING PROTOCOLS
Example : RIPv1 and IGRP Are Classful Routing Protocol.
A Router Running A Classful Routing Protocol Will React In One Of Two Ways When Receiving A Route :
◙ If The Router Has A Directly Connected Interface Belonging To The Same Major Network, It Will Apply The Same Subnet Mask As That Interface.
◙ If The Router Does Not Have Any Interfaces Belonging To The Same Major Network, It Will Apply The Classful Subnet Mask To The Route.
NOTE : When Running A Classful Routing Protocol On A Network, Make Sure You Use The Same Subnet Mask Everywhere. Otherwise, Routing Black Holes Can Occur.
CLASSLESS ROUTING PROTOCOLS : Routing That Sends Subnet Mask Information with their Routing Updates. Classless Routing Allows VLSM (Variable Length Subnet Masking)
Example : RIPv2, EIGRP, OSPF, And BGP Are Classless Routing Protocol.
DYNAMIC ROUTING PROTOCOLS
DYNAMIC ROUTING PROTOCOLS :
In Complex Networks With Multiple Pathways To Destinations, Dynamic Routing Protocols Enable Routers To Advertise Their Networks To Each Other And Dynamically React To Topology Changes.Routing Protocols Determine The Best Path Based On The Lowest Metric.
The Dynamic Routing Method Has Two Parts: ◙ 1. The Routing Protocol That Is Used Between Neighboring Routers To Convey Information About Their Network Environment,
◙ 2. And The Routing Algorithm That Determines Paths Through That Network.
The Protocol Defines The Method Used To Share The Information Externally, Whereas The Algorithm Is The Method Used To Process The Information Internally. The Routing Tables On Dynamic Routers Are Updated Automatically Based On The Exchange Of Routing Information With Other Routers.
THE MOST COMMON DYNAMIC ROUTING PROTOCOLS ARE :
◙ Distance Vector Routing Protocols.◙ Link State Routing Protocols.
Understanding How These Protocols Work Enables You To Choose The Type Of Dynamic Routing That Best Suits Your Network Needs.
DISTANCE VECTOR ROUTING PROTOCOLS
Distance-Vector Routing Protocol Is One Of The Two Major Classes Of Routing Protocols, The Other Major Class Being The Link-State Protocol. Distance-Vector Routing Protocols Use The Bellman-Ford Algorithm, Ford–Fulkerson Algorithm, Or Dual FSM (In The Case Of Cisco Systems's Protocols) To Calculate Paths.
A Distance-Vector Routing Protocol Requires That A Router Informs Its Neighbours Of Topology Changes Periodically. Compared To Link-State Protocols, Which Require A Router To Inform All The Nodes In A Network Of Topology Changes, Distance-Vector Routing Protocols Have Less Computational Complexity And Message Overhead.
Routers Using Distance-Vector Protocol Do Not Have Knowledge Of The Entire Path To A Destination. Instead They Use Two Methods :
◙ 1. Direction In Which Router Or Exit Interface A Packet Should Be Forwarded.
◙ 2. Distance From Its Destination.
Distance-Vector Protocols Are Based On Calculating The Direction And Distance To Any Link In A Network. "Direction" Usually Means The Next Hop Address And The Exit Interface. "Distance" Is A Measure Of The Cost To Reach A Certain Node. The Least Cost Route Between Any Two Nodes Is The Route With Minimum Distance. Each Node Maintains A Vector (Table) Of Minimum Distance To Every Node. The Cost Of Reaching A Destination Is Calculated Using Various Route Metrics. RIP Uses The Hop Count Of The Destination Whereas IGRP Takes Into Account Other Information Such As Node Delay And Available Bandwidth.
Updates Are Performed Periodically In A Distance-Vector Protocol Where All Or Part Of A Router's Routing Table Is Sent To All Its Neighbors That Are Configured To Use The Same Distance-Vector Routing Protocol. RIP Supports Cross-Platform Distance Vector Routing Whereas IGRP Is A Cisco Systems Proprietary Distance Vector Routing Protocol. Once A Router Has This Information It Is Able To Amend Its Own Routing Table To Reflect The Changes And Then Inform Its Neighbors Of The Changes. This Process Has Been Described As ‘Routing By Rumor’ Because Routers Are Relying On The Information They Receive From Other Routers And Cannot Determine If The Information Is Actually Valid And True. There Are A Number Of Features Which Can Be Used To Help With Instability And Inaccurate Routing Information.
EGP And BGP Are Not Pure Distance-Vector Routing Protocols Because A Distance-Vector Protocol Calculates Routes Based Only On Link Costs Whereas In BGP, For Example, The Local Route Preference Value Takes Priority Over The Link Cost.
The Bellman-Ford Algorithm Does Not Prevent Routing Loops From Happening And Suffers From The Count-To-Infinity Problem. The Core Of The Count-To-Infinity Problem Is That If A Tells B That It Has A Path Somewhere, There Is No Way For B To Know If The Path Has B As A Part Of It.
RIP Uses The Split Horizon With Poison Reverse Technique To Reduce The Chance Of Forming Loops And Uses A Maximum Number Of Hops To Counter The 'Count-To-Infinity' Problem. These Measures Avoid The Formation Of Routing Loops In Some, But Not All, Cases. The Addition Of A Hold Time (Refusing Route Updates For A Few Minutes After A Route Retraction) Avoids Loop Formation In Virtually All Cases, But Causes A Significant Increase In Convergence Times.
More Recently, A Number Of Loop-Free Distance Vector Protocols Have Been Developed — Notable Examples Are EIGRP, DSDV And Babel. These Avoid Loop Formation In All Cases, But Suffer From Increased Complexity, And Their Deployment Has Been Slowed Down By The Success Of Link-State Routing Protocols Such As OSPF.
RIPv1:
The Characteristics Of RIPv1 Follow:
Distance-vector protocol.
Uses UDP port 520.
Classful protocol (no support for VLSMs or CIDR).
Metric is router hop count.
Maximum hop count is 15; unreachable routes have a metric of 16.
Periodic route updates broadcast (255.255.255.255) every 30 seconds.
25 routes per RIP message.
Implements split horizon with poison reverse.
Implements triggered updates.
No support for authentication.
Administrative distance for RIP is 120.
Used in small, flat networks or at the edge of larger networks.
RIPv2:
The Characteristics Of RIPv2 Follow:
Distance-vector protocol.
Uses UDP port 520.
Classless protocol (support for CIDR).
Supports VLSMs.
Metric is router hop count.
Maximum hop count is 15; infinite (unreachable) routes have a metric of 16.
Periodic route updates sent every 30 seconds to multicast address 224.0.0.9.
25 routes per RIP message (24 if authentication is used).
Supports authentication.
Implements split horizon with poison reverse.
Implements triggered updates.
Subnet mask included in route entry.
Administrative distance for RIPv2 is 120.
Used in small, flat networks or at the edge of larger networks.
RIPv1 VS RIPv2 :
◙ RIPv2 Can Interoperate With RIPv1. By Default:◙ RIPv1 Routers Will Sent Only Version 1 Packets
◙ RIPv1 Routers Will Receive Both Version 1 And 2 Updates
◙ RIPv2 Routers Will Both Send And Receive Only Version 2 Updates
◙ We Can Control The Version Of RIP A Particular Interface Will “Send” Or “Receive.”
◙ Unless RIPv2 is Manually Specified, A Cisco Will Default To RIPv1 When Configuring RIP.
LINK STATE
WHAT IS LINK-STATES?
OSPF Is A Link-State Protocol. We Could Think Of A Link As Being An Interface On The Router. The State Of The Link Is A Description Of That Interface And Of Its Relationship To Its Neighboring Routers. A Description Of The Interface Would Include, For Example, The IP Address Of The Interface, The Mask, The Type Of Network It Is Connected To, The Routers Connected To That Network And So On. The Collection Of All These Link-States Would Form A Link-State Database.WHAT IS LINK-STATE ALGORITHM?
OSPF Uses A Link-State Algorithm In Order To Build And Calculate The Shortest Path To All Known Destinations. The Algorithm By Itself Is Quite Complicated.The Following Is A Very High Level, Simplified Way Of Looking At The Various Steps Of The Algorithm:
1- Upon Initialization Or Due To Any Change In Routing Information, A Router Will Generate A Link-State Advertisement. This Advertisement Will Represent The Collection Of All Link-States On That Router.
2- All Routers Will Exchange Link-States By Means Of Flooding. Each Router That Receives A Link-State Update Should Store A Copy In Its Link-State Database And Then Propagate The Update To Other Routers.
3- After The Database Of Each Router Is Completed, The Router Will Calculate A Shortest Path Tree To All Destinations. The Router Uses The Dijkstra Algorithm To Calculate The Shortest Path Tree. The Destinations, The Associated Cost And The Next Hop To Reach Those Destinations Will Form The IP Routing Table.
4- In Case No Changes In The OSPF Network Occur, Such As Cost Of A Link Or A Network Being Added Or Deleted, OSPF Should Be Very Quiet. Any Changes That Occur Are Communicated Via Link-State Packets, And The Dijkstra Algorithm Is Recalculated To Find The Shortest Path.
LINK-STATE PROTOCOLS
Link State Routing Protocols, Like Distance Vector Protocols, Are Dynamic. They Propagate Route Information Across Networks. However, They Have A Number Of Advantages Over Distance Vector Protocols.
One Of The Major Advantages Of Link-State Routing Is That They Calculate The Best Route For Data Based On Cost Rather Than Distance. The Algorithms Used To Determine Cost Vary From Protocol To Protocol, But It Is Generally Based On A Link’s Bandwidth. Thus, The Router That The Data Packet Takes To Get To Its Destination Is Optimized.
Additionally, Link State Protocols Do Not Transmit Their Entire Topology Database Across The Network On A Periodic Basis. Once The Network Has Converged, Protocol Traffic Is Limited To Changes In Specific Links (Link State Advertisement Packets) And Keep-Alive Or “Hello” Packets.
Finally, Convergence Times For Link State Protocols Are Generally Much Shorter Than For Distance Vector Protocols. A Network Based On Link-State Routing Will Recognize And Adapt To Failures And Changes Much More Quickly.
There Are A Few Disadvantages To Link State Routing Protocols That Must Be Considered. They Are Generally Much More Complex Than Either Static Routes Or Distance-Vector Routing. This Translates Into Higher Implementation Costs, Higher CPU Utilization, And Greater Memory Requirements.
OSPF HAS THE FOLLOWING FEATURES :
◙ Fast Convergence : OSPF Can Detect And Propagate Topology Changes Faster Than RIP. Count-To-Infinity Does Not Occur With OSPF.◙ Loop-Free Routes : OSPF-Calculated Routes Are Always Loop-Free.
◙ Scalability : With OSPF, An AS Can Be Subdivided Into Contiguous Groups Of Networks Called Areas. Routes Within Areas Can Be Summarized To Minimize Route Table Entries. Areas Can Be Configured With A Default Route Summarizing All Routes Outside The AS Or Outside The Area. As A Result, OSPF Can Scale To Large And Very Large Internetworks. In Contrast, RIP For IP Internetworks Cannot Be Subdivided And No Route Summarization Is Done Beyond The Summarizing For All Subnets Of A Network ID.
◙ Subnet Mask Advertised With The Network: OSPF Was Designed To Advertise The Subnet Mask With The Network. OSPF Supports Variable-Length Subnet Masks (VLSM), Disjointed Subnets, And Supernetting.
◙ Support For Authentication : Information Exchanges Between OSPF Routes Can Be Authenticated. Support For External Routes Routes Outside Of The OSPF AS Are Advertised Within The AS So That OSPF Routers Can Calculate The Least Cost Route To External Networks.
OSPF CHARACTERISTICS AS FOLLOW :
◙ OSPF - ➤ Classless.◙ ALGORITHM - ➤Dijkstra SPF.
◙ METRIC - ➤ Cost (108/Bandwidth BPS).
◙ MAXIMUM HOP COUNT - ➤ None.
◙ AREAS OR AUTONOMOUS SYSTEM CONFIGURATION - ➤ Areas.
◙ HELLO/DEAD TIME - ➤10/40, 30/120.
◙ CISCO OR IETF - ➤IETF.
◙ UPDATESMULTICAST - ➤ (224.0.0.5, 224.0.0.6)
◙ Load Balancing - ➤ Equal Paths.
◙ ROUTED PROTOCOLS - ➤ IP
OSPF Is A Link-State Routing Protocol That Automatically Discovers Its Neighbors By Sending Hello Messages To 224.0.0.5. After The Neighbors Are Discovered, They Form An Adjacency By Synchronizing Their Databases. This Database Lists All Possible Routes That The Neighbor Is Aware Of In The Topology. Each Subnet Learned Has A Cost Associated With It, Which Is Calculated By Taking 108/Bandwidth. The Paths With The Lowest Cost To A Destination Are Put In The Routing Table.
OSPF VS RIP COMPARISON
OSPF Is The First Link-State Routing Protocol That Most People Are Introduced To, So It’s Useful To See How It Compares To More Traditional Distance-Vector Protocols Such As RIPv2 And RIPv1.
| Characteristic | OSPF | RIPv2 | RIPv1 |
|---|---|---|---|
| Type of protocol | Link state | Distance vector | Distance vector |
| Classless support | Yes | Yes | No |
| VLSM support | Yes | Yes | No |
| Auto-summarization | No | Yes | Yes |
| Manual summarization | Yes | No | No |
| Discontiguous support | Yes | Yes | No |
| Route propagation | Multicast on change | Periodic multicast | Periodic broadcast |
| Path metric | Bandwidth | Hops | Hops |
| Hop count limit | None | 15 | 15 |
| Convergence | Fast | Slow | Slow |
| Peer authentication | Yes | Yes | No |
| Hierarchical network | Yes (using areas) | No (flat only) | No (flat only) |
| Updates | Event triggered | Route table updates | Route table updates |
| Route computation | Dijkstra | Bellman-Ford | Bellman-Ford |
RIP HAS CERTAIN LIMITATIONS THAT COULD CAUSE PROBLEMS IN LARGE NETWORKS :
◙ RIP Has A Limit Of 15 Hops. A RIP Network That Spans More Than 15 Hops (15 Routers) Is Considered Unreachable.◙ RIP Cannot Handle Variable Length Subnet Masks (VLSM). Given The Shortage Of IP Addresses And The Flexibility VLSM Gives In The Efficient Assignment Of IP Addresses, This Is Considered A Major Flaw.
◙ Periodic Broadcasts Of The Full Routing Table Will Consume A Large Amount Of Bandwidth. This Is A Major Problem With Large Networks Especially On Slow Links And WAN Clouds.
◙ RIP Converges Slower Than OSPF. In Large Networks Convergence Gets To Be In The Order Of Minutes. RIP Routers Will Go Through A Period Of A Hold-Down And Garbage Collection And Will Slowly Time-Out Information That Has Not Been Received Recently. This Is Inappropriate In Large Environments And Could Cause Routing Inconsistencies.
◙ RIP Has No Concept Of Network Delays And Link Costs. Routing Decisions Are Based On Hop Counts. The Path With The Lowest Hop Count To The Destination Is Always Preferred Even If The Longer Path Has A Better Aggregate Link Bandwidth And Slower Delays.
◙ RIP Networks Are Flat Networks. There Is No Concept Of Areas Or Boundaries. With The Introduction Of Classless Routing And The Intelligent Use Of Aggregation And Summarization, RIP Networks Seem To Have Fallen Behind.
Some Enhancements Were Introduced In A New Version Of RIP Called RIP2. RIP2 Addresses The Issues Of VLSM, Authentication, And Multicast Routing Updates. RIP2 Is Not A Big Improvement Over RIP (Now Called RIP 1) Because It Still Has The Limitations Of Hop Counts And Slow Convergence Which Are Essential In Todays Large Networks.
OSPF, ON THE OTHER HAND, ADDRESSES MOST OF THE ISSUES PRESENTED ABOVE :
◙ With OSPF, There Is No Limitation On The Hop Count.◙ The Intelligent Use Of VLSM Is Very Useful In IP Address Allocation.
◙ OSPF Uses IP Multicast To Send Link-State Updates. This Ensures Less Processing On Routers That Are Not Listening To OSPF Packets. Also, Updates Are Only Sent In Case Routing Changes Occur Instead Of Periodically. This Ensures A Better Use Of Bandwidth.
◙ OSPF Has Better Convergence Than RIP. This Is Because Routing Changes Are Propagated Instantaneously And Not Periodically.
◙ OSPF Allows For Better Load Balancing Based On The Actual Cost Of The Link. Link Delays Are A Major Factor In Deciding Where To Send Routing Updates.
◙ OSPF Allows For A Logical Definition Of Networks Where Routers Can Be Divided Into Areas. This Will Limit The Explosion Of Link State Updates Over The Whole Network. This Also Provides A Mechanism For Aggregating Routes And Cutting Down On The Unnecessary Propagation Of Subnet Information.
◙ OSPF Allows For Routing Authentication By Using Different Methods Of Password Authentication.
◙ OSPF Allows For The Transfer And Tagging Of External Routes Injected Into An Autonomous System. This Keeps Track Of External Routes Injected By Exterior Protocols Such As BGP.
This Of Course Would Lead To More Complexity In Configuring And Troubleshooting OSPF Networks. Administrators That Are Used To The Simplicity Of RIP Will Be Challenged With The Amount Of New Information They Have To Learn In Order To Keep Up With OSPF Networks. Also, This Will Introduce More Overhead In Memory Allocation And CPU Utilization. Some Of The Routers Running RIP Might Have To Be Upgraded In Order To Handle The Overhead Caused By OSPF.
In Many Places, RIP Is Still Used In TCP/IP Networks That Have Not Been Upgraded To OSPF. It Is Also Used On OSPF Networks As An End-Station-To-Router Protocol. OSPF Addresses All The Deficiencies Of RIP, Without Affecting Connectivity To RIP Based Networks. Fast Growing Networks Must Be Designed Properly If The Capabilities Of OSPF Are To Be Fully Exploited. Because Of Its Ability To Handle Variable Networking Masks, OSPF Also Helps To Reduce Waste Of Today's Precious IP Addresses. Ideally, Network Design Should Include A Consistent Enterprise-Wide IP Address Assignment Policy That Lends Itself To The Creation Of OSPF Areas And Address Summarization. If Correct Design And Router-Tuning Takes Place, OSPF Will Allow Networks To Scale To Very Large Topologies, While Maintaining High Levels Of Availability And Performance. Also In The Statement Of RIP Has Slow Convergence Time Is Kind Of Misleading.
OSPF Routes Are Typically More Reliable Than RIP Routes. RIP Only Takes The Number Of Hops Into Account When Computing A Route’s Cost, But OSPF Also Considers The Relative Cost Of Each Link Used In The Route. OSPF Usually Computes The Cost Of A Link Relative To That Link’s Inverse Bandwidth. In Addition, RIP Networks Are Limited To 15 Hops. OSPF Allows Networks To Expand Beyond This Limit.
OSPF Can Also Provide Increased Security. You Can Configure A Router To Require A Clear-Text Or A Message Digest 5 (MD5) Encrypted Key From A Peer Before Exchanging LSAs With It.
ADVANCED DISTANCE VECTOR PROTOCOL
IGRP:
The Characteristics Of IGRP Follow :
Distance-vector protocol.
Uses IP protocol 9.
Classful protocol (no support for CIDR).
No support for VLSMs.
Composite metric of bandwidth and delay.
You can factor load and reliability into the metric.
Route updates broadcast every 90 seconds.
104 routes per IGRP message.
No support for authentication.
Implements split horizon with poison reverse.
Implements triggered updates.
By default, equal-cost load balancing. Unequal-cost load balancing with the variance command.
Administrative distance is 100.
Previously used in large networks; now replaced by EIGRP.
THE CHARACTERISTICS OF EIGRP :
Hybrid Routing Protocol (Distance Vector That Has Link-State Protocol Characteristics).
Uses IP protocol 88.
Classless Protocol (Supports VLSMs).
DEFAULT COMPOSITE METRIC OF BANDWIDTH AND DELAY.
You Can Factor Load And Reliability Into The Metric.
Sends Route Updates To Multicast Address 224.0.0.10.
Sends Partial Route Updates Only When There Are Changes.
Support For Authentication.
Uses DUAL For Loop Prevention.
By Default, Equal-Cost Load Balancing. Unequal-Cost Load Balancing With The Variance Command.
Administrative Distance Is 90 For EIGRP Internal Routes, 170 For EIGRP External Routes, And 5 For EIGRP Summary Routes.
Potential Routing Protocol For The Core Of A Network; Used In Large Networks.
In The EIGRP Topology Table, EIGRP Maintains The Advertised Distance And The Feasible Distance To Every Subnet. The Subnet(S) With The Lowest Feasible Distance Is The Route That Is Placed In The Routing Table Known As The Successor Route. If The Advertised Distance Of An Alternative Route Is Lower Than The Feasible Distance Of The Successor Route, It Is A Feasible Successor, Which Is Used If The Successor Route Fails. This Is Why EIGRP’s DUAL Algorithm Makes It The Fastest-Converging Routing Protocol.
OSPF VS EIGRP COMPARISON
The Open Shortest Path First Protocol Is An “Open Standard.” This Means That It Can Be Implemented On Any Platform, From Any Vendor Or Manufacturer. This Is An Advantage Over Enhanced Interior Gateway Protocol, Which Is A Proprietary Standard From Cisco. However, This Is The Only Clear Advantage Of OSPF Over EIGRP.
As Previously Stated, OSPF Is Designed Primarily For Hierarchical Networks With A Clearly Defined Backbone Area. This Is Clearly Not The Case In The
Enhanced Interior Gateway Protocol Is A Proprietary Routing Protocol Developed By Cisco And Used Exclusively In Their Routing Products. Although It Is Often Lumped In With OSPF As A Link State Protocol, It Is Actually A Hybrid; Containing The Best Elements Of Both Link State And Distance Vector Protocols.
EIGRP, As Stated Previously, Has Several Advantages Over OSPF When Used In The
◙ Improved Router Memory And CPU Utilization When Compared To OSPF.
◙ Intelligent Bandwidth Control – EIGRP Takes Into Consideration The Available Bandwidth When Determining The Rate At Which It Will Transmit Updates. Interfaces Can Also Be Configured To Use A Certain (Maximum) Percentage Of The Bandwidth, So That Even During Routing Topology Computations, A Defined Portion Of The Link Capacity Remains Available For Data Traffic.
◙ EIGRP Does Not Require A Hierarchical Network Design To Operate Efficiently. It Will Automatically Summarize Routes Where Applicable.
◙ Unlike OSPF, Which Only Takes Bandwidth Into Consideration When Calculating The Cost Of A Route, EIGRP Can Be Configured To Use Bandwidth, Delay, Reliability, And Load When Calculating Optimum Routes. This Has Proven To Be A Valuable Consideration In A Wireless Environment.
◙ EIGRP Has Greater Control On Timing Issues, Such As Hold Times And Hello Intervals, Than Does OSPF. This Allows Greater Flexibility With Wireless Connections, Where These Intervals Must Be Fine-Tuned To A Particular Device Or Bandwidth.
◙ EIGRP Is Less Complex And Has Less Cost (Manpower And Time) Involved In Configuration And Administration.
◙ Although EIGRP Is Proprietary, It Can Communicate And Redistribute Routing Information With Other Routing Protocols, Such As OSPF. This Is Accomplished Through Router Redistribution Or Using An Exterior Routing Protocol Such As BGP.
EIGRP AND OSPF COMPARISON TABLE:
PATH VECTOR PROTOCOLS
The Border Gateway Protocol (BGP) Is An Inter-Autonomous System Routing Protocol. An Autonomous System (AS) Is A Network Or Group Of Networks Under A Common Administration And With Common Routing Policies. BGP Is Used To Exchange Routing Information For The Internet And Is The Protocol Used Between Internet Service Providers (ISP), Which Are Different ASes. One Of The Most Important Characteristics Of BGP Is Its Flexibility. The Protocol Can Connect Together Any Internetwork Of Autonomous Systems Using An Arbitrary Topology. The Only Requirement Is That Each AS Have At Least One Router That Is Able To Run BGP And That This Router Connect To At Least One Other AS's BGP Router. Beyond That, “The Sky's The Limit,” As They Say. BGP Can Handle A Set Of Ass Connected In A Full Mesh Topology(Each AS To Each Other AS), A Partial Mesh, A Chain Of ASes Linked One To The Next, Or Any Other Configuration. It Also Handles Changes To Topology That May Occur Over Time.
The Primary Function Of A BGP Speaking System Is To Exchange Network Reachability Information With Other BGP Systems. This Network Reachability Information Includes Information On The List Of Autonomous Systems (ASs) That Reachability Information Traverses. BGP Constructs A Graph Of Autonomous Systems Based On The Information Exchanged Between BGP Routers. As Far As BGP Is Concerned, Whole Internet Is A Graph Of Ass, With Each AS Identified By A Unique AS Number. Connections Between Two Ass Together Form A Path And The Collection Of Path Information Forms A Route To Reach A Specific Destination. BGP Uses The Path Information To Ensure The Loop-Free Inter-Domain Routing.
Another Important Assumption That BGP Makes Is That It Doesn't Know Anything About What Happens Within The AS. This Is Of Course An Important Prerequisite To The Notion Of An AS Being Autonomous - It Has Its Own Internal Topology And Uses Its Own Choice Of Routing Protocols To Determine Routes. BGP Only Takes The Information Conveyed To It From The AS And Shares It With Other ASs.
When A Pair Of Autonomous Systems Agrees To Exchange Routing Information, Each Must Designate A Router That Will Speak BGP On Its Behalf; The Two Routers Are Said To Become BGP Peers Of One Another. As A Router Speaking BGP Must Communicate With A Peer In Another Autonomous System, Usually A Machine, Which Is Near To The Edge (Border) Of The Autonomous System Is Selected For This. Hence, BGP Terminology Calls The Machine A Border Gateway Router.
BGP CHARACTERISTICS :
BGP Is Different From Other Routing Protocols In Several Ways. Most Important Being That BGP Is Neither A Pure Distance Vector Protocol Nor A Pure Link State Protocol. BGP Is An Exterior Gateway Protocol (EGP) Used In Routing In The Internet. It Is An Interdomain Routing Protocol.◙ BGP Is A Path Vector Routing Protocol Suited For Strategic Routing Policies.
◙ BGP Uses TCP Port 179 To Establish Connections With Neighbors (BGP Uses TCP For All Communication. So The Reliability Issues Are Taken Care By TCP.).
◙ BGPv4 Implements CIDR.
◙ EBGP Is For External Neighbors. It's Used Between Separate Autonomous Systems.
◙ IBGP Is For Internal Neighbors. It's Used Within An AS.
◙ BGP Uses Several Attributes In The Routing-Decision Algorithm.
◙ BGP Uses Confederations And Route Reflectors To Reduce BGP Peering Overhead.
◙ The MED (Metric) Attribute Is Used Between Autonomous Systems To Influence Inbound Traffic.
◙ Weight Is Used To Influence The Path Of Outbound Traffic From A Single Router, Configured Locally.
◙ Security, BGP Allows A Receiver To Authenticate Messages, So That The Identity Of The Sender Can Be Verified.
OSPF VS BGP COMPARISON
The OSPF Will Always Search For The Fastest Route, And Not The Shortest, In Spite Of Its Name. Routers Using The OSPF Protocol Will Verify The Status Of The Other Routers To Which They Have Access, Frequently Sending A Message. From This, They Can Ascertain A Router’s Status, And Whether It Is Online. In Regards To OSPF, Routers Will Know All The Available Paths Possible, Not Only The Shortest, And They Will Also Permit Load Balancing, Where A Router May Split The Datagram Evenly Between The Available Paths To A Destination. OSPF Is Mainly Used On Smaller Scale Networks That Are Centrally Administered.
The BGP Protocol Is Mainly Used On Very Large-Scale Networks, Like The Internet. As Such, Routers On The Internet Use BGP Protocol, And It Is Classified As An External Gateway Protocol, While OSPF Is An Internal Gateway Protocol. BGP Can Either Be Internal Or External. Internal BGP Is Where The Protocol Is Used By A Collection Of Routers And Client Machines Under The Same Administration Unit, Which Is Known As An Autonomous System. The External BGP Is Where The Protocol Is Running Under Two Autonomous Systems That Are Different.
BGP Is More Complicated Than OSPF, As It Employs Various Attributes In Determining The Best Path For A Datagram.
SUMMARY
Maximum Hop Counts:
MAXIMUM HOP COUNTS:
◙ RIPv1 -> Distance - > vector15 (Maximum Hop Count).◙ RIPv2 - > Distance - > vector15 (Maximum Hop Count).
◙ EIGRP - > Hybrid - > 224 (Maximum Hop Count).
◙ OSPF - > Link - > stateInfinite (Maximum Hop Count).
Split Horizon: Subnets Learned From Neighbor Routers Should Not Be Sent Back Out The Same Interface From Which The Original Update Came.
Route Poisoning With Poison Reverse: When A Route To A Subnet Fails, The Subnet Is Advertised With An Infinite Metric. Routers Receiving The Poisoned Route Override The Split Horizon Rule And Send A Poison Reverse Back To The Source.
Hold-down timers: The Amount Of Time A Router Ignores Any Information About An Alternative Route With A Higher Metric To A Poisoned Subnet.
Flash updates/triggered updates: When A Route Fails, The Router Immediately Shoots Out An Update As Opposed To Waiting For A Normal Update Interval.
NOTE : ◙ Redistribution : Redistribution Imports Routes From One Protocol To Another. Redistribution Sends Route Updates For A Protocol-Based Route Through Another Protocol.
CONCLUSION:
The Goal Of This Article Is To Give An Easy Way To Understand The “DIFFERENCE BETWEEN OSPF VS EIGRP, BGP AND RIP". 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, MCSE, MCSA, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+.
DISCLAIMER:
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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IGRP, EIGRP, OSPF, ISIS, BGP
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