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All slides are customized by Engr. Vernon Degala. For educational purposes only.All slides are customized by Engr. Vernon Degala. For educational purposes only.
Module 7: Distance Vector Routing Protocols
– RIP & IGRP
inspired by Cisco Networking Academy Computer Networks and Security CCNA 2: Routers and Routing Basics
ORIGINAL COPY
Distance vector routing updates
• Routing table updates occur periodically or
when topology change
• Routers send their entire routing table to all
adjacent neighbors
• Routing table contains info about routing
metrics
- Hop count
- Bandwidth
- Cost
- Load
- Reliability
- Delay
- Loops occur when inconsistent routing tables are
not updated due to slow convergence in a
changing network
All slides are customized by Engr. Vernon Degala. For educational purposes only. Count To Infinity
- Count to infinity
- Packets loop continuously around the network
- Packet never reach their destination
- May occur because
- Network is down
- Interface not configured correctly
- To overcome count to infinity
- Specify a maximum hop count
- Split Horizon
- Route Poisoning
- Hold Down timers Maximum hop count
- Used to overcome count to infinity
- Hop count
- The number of routers a
packet goes through
packet goes through a
router
- RIP maximum hop count is 15 - Packet is discarded if the
hop count of 16 is reached
network 1 is unreachable
All slides are customized by Engr. Vernon Degala. For educational purposes only. Configuring RIP
- Enter global configuration mode
- Specify RIP as the routing protocol
- Router(config)#router rip
- Specify directly connected networks
- Router(config-router)#network 10.10.10.
- A router running RIP can be configured to
- Send triggered updates independently the scheduled updates (every 30 seconds)
- Router(config-if)#ip rip triggered
- To prevent RIP updates leaving an interface
- Router(config-router)#passive-interface Fa0/
- To configure RIP to exchange routing information in a non-broadcast network (Frame Relay) - RIP needs to be told of other neighboring RIP routers - Router(config-router)#neighbor - To configure software to send and receive Rip V1 and V packets - Router(config-router)# version{1|2} - To configure an interface to send RIP V1 packets - Router(config-if)# ip rip send version 1 - To configure an interface to send RIP V2 packets - Router(config-if)# ip rip send version 2 - To configure an interface to send RIP V1 and V2 packets - Router(config-if)# ip rip send version 1 2 - To configure and interface to receive RIP V1 packets - Router(config-if)# ip rip receive version 1 - To configure and interface to receive RIP V2 packets - Router(config-if)# ip rip receive version 2 - To configure and interface to receive RIP V1 and V2 packets - Router(config-if)# ip rip receive version 1 2
All slides are customized by Engr. Vernon Degala. For educational purposes only.
Preventing routing updates through an interface
• network command
- If it is issued for a given network using RIP or IGRP
- router immediately begin sending advertisements out all interfaces within the specified network
address range
- Router(config)#router RIP
- Router(config-router)#network 192.101.21.
• passive interface command
- Stops the router from sending updates through a particular interface to a neighbor
- Router continues to listen and use routing updates from that neighbor
- Prevent other systems from learning about routes dynamically
- Router(config)#router RIP
- Router(config-router)#passive-interface fa0/
All slides are customized by Engr. Vernon Degala. For educational purposes only. IGRP features
- Distance vector routing protocol
- Developed by Cisco
- Sends routing updates every 90 second
- Advertising networks for an autonomous
system
- Metrics used are normally bandwidth and
delay
- Bandwidth
- Delay – amount of time to get to the destination
- Reliability – reliability of link determined by exchange of keepalives
- Load
- MTU – maximum transmission unit of the path
- IGRP converges faster than RIP
- thereby avoiding the routing loops
- IGRP does not share the hop count limitation of RIP.
- Useful Commands
- show interface interface
- show running-config
- show running-config interface interface
- show running-config | begin interface interface
- show running-config | begin igrp
- show ip protocols IGRP Routes
- IGRP advertises three types of routes:
- Interior
- Routes between subnets of a network attached to a router interface
- If the network attached to a router is not subnetted, IGRP does not advertise interior routes
- System
- Routes to networks within an autonomous system number
- The IOS derives system routes from directly connected network interfaces
- System routes information provided by other IGRP routers.
- System routes do not include subnet information
- Exterior
- Routes to networks outside the autonomous system that are considered when identifying a gateway of last resort.
- Gateway of last resort is used if
- a better route is not found
- The destination is not a connected network
- Exterior routes are also referred to as "candidate default"
All slides are customized by Engr. Vernon Degala. For educational purposes only. IGRP stability features Holddowns Prevent regular update messages from inappropriately reinstating a route that may not be up Split horizons
- It is usually not useful to send information about a route back in the direction from which it came
- Prevent routing loops Poison reverse
- Poison reverse updates then are sent to remove the route and place it in holddown.
- With IGRP, poison reverse updates are sent only if a route metric has increased by a factor of 1.1 or greater. IGRP Timers
- update timer specifies
- how frequently routing update messages should be sent
- Default is 90 sec
- invalid timer specifies
- how long a router should wait in the absence of routing-update messages about a route before declaring that route invalid
- Default is 3 times the update period (270 sec)
- holddown timer specifies
- the amount of time for which information about poorer routes is ignored
- Default is 3 times the update timer period + 10 sec (280 sec)
- flush timer indicates
- how much time should pass before a route is flushed from the routing table
- Default is 7 times the routing update timer (after 630 sec)
