distance vector routing protocols dynamic routing
TRANSCRIPT
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 ApproachesDistance Vector Protocols
E.g., RIP (Routing Information Protocol)
Link State ProtocolsE.g., OSPF (Open Shortest Path First)
Our FocusDistance Vector Protocols - RIP
Routing Protocols- Criteria to compare
Criteria used to compare routing protocols includes
Time to convergence Scalability Resource usage Implementation & maintenance
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 MaintenanceTriggered Updates
Conditions in which triggered updates are sentInterface changes
stateRoute becomes
unreachableRoute is placed in
routing table
Network Discovery Initial Exchange of Routing
InformationIf a routing protocol is configured
then routers will exchange routing information
Routing updates received from other routersRouter checks update for new
informationIf there is new information
Metric is updatedNew 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
ConvergenceExchange of Routing
InformationRouter convergence is
reached whenAll routing tables in the
network contain the same network information
Routers continue to exchange routing informationIf 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.
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
AA BB CC1 1
A's Routing Table B's Routing Table
C
to costvia(next hop)
2B C
to costvia(next hop)
1C
now link B-C goes down
C 2 C oo
C oo-C 2B
C oo C 3
C 3AC oo-
C 4 C oo
C oo-C 4B
• 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?