EIGRP Graceful Shutdown - Goodbye Message

EIGRP Graceful shutdown is designed to improve EIGRP network convergence and it uses Goodbye message to communicate this information to the neighbors.

Let's try to understand the concept using above topology.

If R1 has to go down for some maintenance, R2 would have to wait for its hold timer to expire before it would discover the change and react to it.Packets sent during this time would be lost.

With graceful shutdown feature in EIGRP, a Goodbye message is multicast when an EIGRP routing process is shut down, to inform adjacent peers about this topology change. This feature allows supporting EIGRP peers to synchronize and recalculate neighbor relationships more efficiently than would occur if the peers discovered the topology change after the hold timer expired. The Goodbye message is supported in Cisco IOS Software Release 12.3(2), 12.3(3)B, and 12.3(2)T and later.

In above lab simulation, I have used 12.4 IOS version.

To simulate the generation of Goodbye message, I have removed the network command on R1 and we can see that a Goodbye message is received on R2.

R1(config)# router eigrp 10
R1(config-router)#no network

*Mar  1 00:05:18.111: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor (FastEthernet0/0) is down: Interface Goodbye received

Imp Note: Goodbye messages are sent in hello packets. EIGRP sends an interface goodbye message with all K values set to 255 when taking down all peers on an interface.

A Cisco router that runs IOS release (12.2 for example) that does not support the Goodbye message will not be able interpret the message as a K-value mismatch and therefore display the following message:

*Mar  1 00:08:18.411: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor (FastEthernet0/0) is down: K-value mismatch

The receipt of a goodbye message by a non-supporting neighbor does not disrupt normal network operation of EIGRP. The non-supporting neighbor will terminate the session when the hold timer expires. The sending and receiving routers will re-converge normally after the sender reloads.

An EIGRP router will send a Goodbye message on an interface if the network command (under the EIGRP process) that encompasses the network on that interface is removed (with 'no network' router  config command). An EIGRP router sends a goodbye message on all interfaces if the EIGRP process is shut down (with 'no router eigrp AS Number' global config command). However, an EIGRP router will not send a Goodbye message if an interface is shut down or the router is reloaded.

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