EIGRP Graceful Shutdown

EIGRP Graceful Shutdown feature is designed to improve EIGRP network convergence and it uses Goodbye message to communicate this information to the neighbors. Using Graceful Shutdown in EIGRP feature, a Goodbye Message is broadcasted 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-Parameter values set to 255 when taking down all peers on an interface. Let us understand this concept with a help of lab simulation as shown below.

 

EIGRP Graceful Shutdown - Scenario1

When Cisco router supports EIGRP Goodbye Message

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 the above lab simulation, I have used a Cisco 3725 serious router with a 12.4 IOS version.

To simulate the generation of EIGRP Goodbye message, I have removed the network 10.0.0.0 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    

The following message is received at router R2 if it supports goodbye messages.

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           

                                                                          

                       

The below Wireshark capture shows EIGRP Goodbye message sent by router R1 to R2 with all EIGRP K Parameter values are set to 255. Again to reiterate that Goodbye Message is sent in EIGRP Hello Message.

 

EIGRP Graceful Shutdown - Scenario2

When A Cisco router does not support EIGRP Goodbye Message

Note: The goodbye message is supported in Cisco IOS Software Release 12.3(2), 12.3(3)B, and 12.3(2)T and later.

A Cisco router that runs IOS release (12.2 or lesser for example) that does not support the EIGRP Goodbye message feature will not be able to 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.

When EIGRP Goodbye Message is generated?

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.

EIGRP 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.
  

 

I hope you have found this article informative and useful and now have a fair understanding of EIGRP Graceful Shutdown and EIGRP Goodbye Message. For any of the related queries or feedback, kindly write to us at networkurge@gmail.com

 

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