Distance Vector Routing Protocols Dynamic Routing

Objectives Characteristics of Distance Vector Routing protocols. Network discovery process using Routing Information Protocol (RIP). Identify the conditions leading to a routing loop and explain the implications for router performance.

Review - Dynamic Routing Protocols Function(s) of Dynamic Routing Protocols: Dynamically share information between routers. Automatically update routing table when topology changes. Determine best path to a destination.

Interior Gateway Routing Two Main Approaches Distance Vector Protocols E.g., RIP (Routing Information Protocol) Link State Protocols E.g., OSPF (Open Shortest Path First) Our Focus Distance Vector Protocols - RIP

Routing Protocols- Criteria to compare Criteria used to compare routing protocols includes  Time to convergence  Scalability  Resource usage  Implementation & maintenance

Routing Protocol Algorithm Algorithm - procedure for accomplishing a certain task

Distance Vector Routing Protocols A router using distance vector routing protocols knows 2 things:  Distance to final destination  Vector, or direction, traffic should be directed

Distance Vector Routing Protocols Characteristics  Periodic updates  Triggered updates  Exchange information with Neighbors  Entire routing table is included with routing update

Routing Table Maintenance Triggered Updates Conditions in which triggered updates are sent Interface changes state Route becomes unreachable Route is placed in routing table

Network Discovery Initial Exchange of Routing Information If a routing protocol is configured then routers will exchange routing information Routing updates received from other routers Router checks update for new information If there is new information Metric is updated New information is stored in routing table

Routing Table - Periodic Updates Regular Time Intervals in which a router sends out its entire routing table to its neighbours.

Routing Table Maintenance RIP uses 4 timers - Update timer -Invalid timer -Holddown timer -Flush timer

Convergence Exchange of Routing Information Router convergence is reached when All routing tables in the network contain the same network information Routers continue to exchange routing information If no new information is found then Convergence is reached

RIP Commands Using router rip and network commands to enable RIP. Enabling RIP on an IP-addressed network. Monitoring IP packet flow using the show IP protocol command. The show ip route command.

Configuring RIP

The show ip protocols Command

Troubleshooting RIP Update Issues debug ip rip show ip rip database show ip protocols {summary} show ip route debug ip rip {events} show ip interface brief

18 The Count-to-Infinity Problem A A B B C C 11 The reason for the count-to-infinity problem is that each node only has a “next-hop-view” For example, in the first step, A did not realize that its route (with cost 2) to C went through node B How can the Count-to- Infinity problem be solved?

Preventing Routing Updates through an Interface

Load Balancing with RIP