EIGRP is one of the routing protocols commonly used in large enterprise networks. Modifying EIGRP features and troubleshooting problems is one of the most essential skills for a network engineer involved in the implementation and maintenance of large routed enterprise networks that use EIGRP.
Summarization decreases the number of entries in routing updates and lowers the number of entries in local routing tables. It also reduces bandwidth utilization for routing updates and results in faster routing table lookups. EIGRP for IPv4 autosummarization is disabled by default beginning with Cisco IOS Release 15.0(1)M and 12.2(33). Prior to this, autosummarization was enabled by default. To enable autosummarization for EIGRP use the auto-summary command in router configuration mode. Use the show ip protocols command to verify the status of autosummarization. Examine the routing table to verify that autosummarization is working.
EIGRP automatically includes summary routes to Null0 to prevent routing loops that are included in the summary but do not actually exist in the routing table. The Null0 interface is a virtual IOS interface that is a route to nowhere, commonly known as "the bit bucket." Packets that match a route with a Null0 exit interface are discarded.
To establish EIGRP manual summarization on a specific EIGRP interface, use the following interface configuration mode command:
Router(config-if)# ip summary-address eigrp as-number network-address subnet-mask
To configure EIGRP for IPv6 manual summarization on a specific EIGRP interface, use the following interface configuration mode command:
Router(config-if)# ipv6 summary-address eigrp as-number prefix/prefix-length
One method of propagating a default route within the EIGRP routing domain is to use the redistribute static command. This commandtells EIGRP to include this static route in its EIGRP updates to other routers. The show ip protocols command verifies that static routes within the EIGRP routing domain are being redistributed.
Use the ip bandwidth-percent eigrp as-number percent interface configuration mode command to configure the percentage of bandwidth that can be used by EIGRP on an interface.
To configure the percentage of bandwidth that can be used by EIGRP for IPv6 on an interface, use the ipv6 bandwidth-percent eigrp command in interface configuration mode. To restore the default value, use the no form of this command.
Hello intervals and Hold times are configurable on a per-interface basis in EIGRP and do not have to match with other EIGRP routers to establish or maintain adjacencies.
For IP in EIGRP, Cisco IOS software applies load balancing using up to four equal-cost paths by default. With the maximum-paths router configuration mode command, up to 32 equal-cost routes can be kept in the routing table.
EIGRP supports routing protocol authentication using MD5. The algorithms and the configuration to authenticate EIGRP for IPv4 messages are the same as EIGRP for IPv6. The only difference is that the interface configuration mode commands use ip, instead of ipv6.
Router(config-if)# ipv6 authentication mode eigrp as-number md5
Router(config-if)# ipv6 authentication key-chain eigrp as-number name-of-chain
To verify that the correct EIGRP adjacencies were formed after being configured for authentication, use the show ip eigrp neighbors command on each router.
The show ip route command verifies that the router learned EIGRP routes. The show ip protocols command is used to verify that EIGRP displays the currently configured values.