EIGRP Auto Summarization

EIGRP Auto Summarization

Router(config-router)#no auto-summary	Turns off the auto-summarization feature. Networks are summarized at the classful boundary by default
Router(config)#int fa 0/0
Router(config-if)ip summary-address eigrp 100 10.10.0.0 255.255.0.0	Enables manual summarization on this specific interface for the given address and mask

Caution:

EIGRP automatically summarizes networks at the classful boundary. A poorly designed network with discontiguous subnets could have problems with connectivity if the summarization feature is left on. You could have two routers advertise the same network172.16.0.0/16when in fact the intention is for the routers to advertise two different networks172.16.10.0/24 and 172.16.20.0/24.

Recommended practice is that you turn off automatic summarization, use the ip summary-address command, and summarize manually what you need to.

Configuring EIGRP

Configuring EIGRP

Router(config)#router eigrp 100	Turns on the EIGRP process
	100 is the autonomous system (AS) number, which can be a number between 1 and 65535
	All routers in the same AS must use the same AS number
Router(config-router)#network 10.0.0.0	Specifies which network to advertise in EIGRP
Router(config-router)#eigrp log-neighbor-changes	Logs any changes to an EIGRP neighbor adjacency

Tip:

The eigrp log-neighbor-changes command, although optional, is recommended to help with troubleshooting.

Router(config-router)#no network 10.0.0.0	Removes the network from the EIGRP process
Router(config)#no eigrp 100	Disables routing process 100
Router(config-if)#bandwidth x	Sets the bandwidth of this interface to x kilobits to allow EIGRP to make a better routing decision

Tip:

The bandwidth command is used for metric calculations only. It does not change interface performance.

Configuration Example: RIP Ver 2 Routing

Configuration Example: RIP-2 Routing

Figure A shows the network topology for the configuration that follows, which shows how to configure RIP-2 using the commands covered in this chapter.

Figure 8-1. Network Topology for RIP-2 Routing Configuration

Boston Router

Boston>en
Boston#config t
Boston(config)#router rip	Enables RIP routing
Boston(config-router)#version 2	Enables RIP-2
Boston(config-router)#network 172.16.0.0	Advertises directly connected networks (classful address only)
Boston(config-router)#no auto-summary	Turns off autosummarization
Boston(config-router)#exit
Boston(config)#exit
Boston#copy run start

Buffalo Router

Buffalo>en
Buffalo#config t
Buffalo(config)#router rip	Enables RIP routing
Buffalo(config-router)#version 2	Enables RIP-2
Buffalo(config-router)#network 172.16.0.0	Advertises directly connected networks (classful address only)
Buffalo(config-router)#no auto-summary	Turns off autosummarization
Buffalo(config-router)#Cntl+z	Exits back to privileged mode
Buffalo#copy run start

Bangor Router

Bangor>en
Bangor#config t
Bangor(config)#router rip	Enables RIP routing
Bangor(config-router)#version 2	Enables RIP-2
Bangor(config-router)#network 172.16.0.0	Advertises directly connected networks (classful address only)
Bangor(config-router)#no auto-summary	Turns off autosummarization
Bangor(config-router)#Cntl+z	Exits back to privileged mode
Bangor#copy run start