IT Certification and Training Blog

A Case Study on EIGRP Graceful Shutdown

Posted by Kelson Lawrence on Feb 8, 2011 10:25:00 AM

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:

Router1#show running-config
hostname Router1
interface FastEthernet0/0  
 ip address 10.0.0.1 255.255.255.0
router eigrp 100  
 network 10.0.0.0

Router2#show running-config
hostname Router2
interface FastEthernet0/0  
 ip address 10.0.0.2 255.255.255.0
router eigrp 100  
 network 10.0.0.0

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:

Frame 162 (74 bytes on wire, 74 bytes captured)
Ethernet II, Src: cc:00:15:7c:00:00 (cc:00:15:7c:00:00), Dst: IPv4mcast_00:00:0a (01:00:5e:00:00:0a)
Internet Protocol, Src: 10.0.0.1 (10.0.0.1), Dst: 224.0.0.10 (224.0.0.10)
Cisco EIGRP
    Version = 2
    Opcode = 5 (Hello)
    Checksum = 0xf168
    Flags = 0x00000000
    Sequence = 0
    Acknowledge = 0
    Autonomous System : 100
    EIGRP Parameters
        Type = 0x0001 (EIGRP Parameters)
        Size = 12 bytes
        K1 = 255
        K2 = 255
        K3 = 255
        K4 = 255
        K5 = 255
        Reserved
        Hold Time = 15
    Software Version: IOS = 12.3, EIGRP = 1.2
        Type = 0x0004 (Software Version)
        Size = 8 bytes
        IOS release version = 12.3
        EIGRP release version = 1.2
 

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.

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Tags: Andrew Messier, EIGRP, graceful shutdown, router, Eigrp graceful shutdown, case study, router protocols