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EIGRP Graceful Shutdown - Goodbye Message

EIGRP Graceful Shutdown - Goodbye Message - Concept


EIGRP Graceful shutdown is designed to improve EIGRP network convergence and it uses Goodbye message to communicate this information to the neighbors. With graceful shutdown, a goodbye message is broadcast when an EIGRP routing process is shut down, to inform adjacent peers about the impending 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.

Goodbye messages are sent in EIGRP Hello packets. EIGRP sends an interface goodbye message with all K values set to 255 when taking down all peers on an interface.
EIGRP Graceful Shutdown

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

To simulate the generation of EIGRP 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 10.0.0.0

R2#
*Mar  1 00:05:18.111: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 10.10.12.1 (FastEthernet0/0) is down: Interface Goodbye received


EIGRP Goodbye Message - K Parameters

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 10.10.12.1 (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 the no network command). An EIGRP router sends a goodbye message on all interfaces if the EIGRP process is shut down (with the no router eigrp command). An EIGRP router will not, however, send a goodbye message if an interface is shut down or the router is reloaded.

Additional Information - EIGRP Useful commands:

  • show ip eigrp neighbors - Displays neighbors discovered by EIGRP.
  • show ip route - Displays the current entries in the IP routing table for all configured routing protocols.
  • show ip route eigrp - Displays the current EIGRP entries in the IP routing table.
  • show ip protocols - Displays the parameters and current state of the active routing protocol processes. For EIGRP, this command shows the EIGRP autonomous system number, filtering and redistribution numbers, and neighbors and distance information.
  • show ip eigrp interfaces - Displays information about interfaces configured for EIGRP.
  • show ip eigrp topology - Displays the EIGRP topology table. This command shows the topology table, the active or passive state of routes, the number of successors, and the FD to the destination. Note that only successor and feasible successor routes are displayed; add the all-links keyword to display all routes, including those not eligible to be successor or feasible successor routes.
  • show ip eigrp traffic - Displays the number of EIGRP packets sent and received. This command displays statistics on hello packets, updates, queries, replies, and acknowledgments.
  • debug eigrp packets -  Displays the types of EIGRP packets sent and received. A maximum of 11 packet types can be selected for individual or group display.
  • debug ip eigrp - Displays packets that are sent and received on an interface. Because this command generates large amounts of output, use it only when traffic on the network is light.
  • debug ip eigrp summary  - Displays a summarized version of EIGRP activity. It also displays filtering and redistribution numbers and neighbors and distance information.
  • debug eigrp neighbors - Displays neighbors discovered by EIGRP and the contents of the hello packets.

 

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