By Andrew Messier
The topology for this study consists of two routers connected on a LAN. FastEthernet 0/0 on Router1 connects to FastEthernet 0/0 on Router2. Full connectivity exists between both routers, and Enhanced Interior Gateway Routing Protocol (EIGRP) using Autonomous System (AS) 100 is configured to run on both FastEthernet ports. Below is sample configuration for this setup:
ip address 10.0.0.1 255.255.255.0
router eigrp 100
ip address 10.0.0.2 255.255.255.0
router eigrp 100
What is a graceful shutdown, what do the contents of an EIGRP packet look like when the message is sent, and what does the receiving router do with the message?
A graceful shutdown is a router’s way of telling its neighbor to end the adjacency with the router because the EIGRP routing process is disabled. The change converges more quickly than allowing each device to reach its hold interval, which is by default fifteen seconds on fast links. A graceful shutdown is a goodbye message sent out of each interface running EIGRP. The goodbye message is a form of a Hello message, but with all five K-values set to 255. Below is sample capture after removing EIGRP from interface FastEthernet 0/0 on Router1:
When the command eigrp log-neighbor-changes in EIGRP-configuration mode is enabled, routers that had adjacencies with the router sending the graceful shutdown may print out one of two things depending on what Cisco IOS Release is running. Cisco IOS did not support the goodbye message until release 12.3, so devices using older IOS will display that a K-Value mismatch was found, and devices since the update will display the receipt of the goodbye message. In either case, the device receiving the message will disable the EIGRP adjacency established with the sending neighbor on that interface.