邻居检查key是不是和它自己的配置key匹配（共享密钥）.
配置key (密码) 和 key ID; router对key和key id进行一个
hash的计算，生成一个值，这个值就是一个消息摘要，消息摘
要随EIGRP报文一起发送，但是key（密码）不发送.
处理会加密，理论上哈希算法是不可破解的，也是不可逆的算法。
11(key)+22(key id) 哈希计算 形成一个值=cisco
路由器根据key，key ID以及信息产生消息的哈希值
指定 key ID (号码), key和key的生命周期.
首先使用第一个有效的 key, 然后依key的号码顺序使用。.
Router(config)#key chain name-of-chain
Router(config-keychain)#key key-id
Router(config-keychain-key)#key-string text
Router(config-keychain-key)#accept-lifetime start-time {infinite | end-time | duration seconds} 可选项: 指定对接收到的包什么时候采用这个key
Router(config-keychain-key)#send-lifetime start-time {infinite | end-time | duration seconds} 可选项: 指定对发出去的包什么时候采用这个key
Router(config-if)#ip authentication mode eigrp autonomous-system md5 指定EIGRP的包采用 MD5 认证
Router(config-if)#ip authentication key-chain eigrp autonomous-system name-of-chain 允许 EIGRP 的包通过 keychain 中指定的key进行认证
accept-lifetime 04:00:00 Jan 1 2006 infinite
send-lifetime 04:00:00 Jan 1 2006 04:01:00 Jan 1 2006
accept-lifetime 04:00:00 Jan 1 2006 infinite
send-lifetime 04:00:00 Jan 1 2006 infinite
interface FastEthernet0/0
ip address 172.16.1.1 255.255.255.0
ip address 192.168.1.101 255.255.255.224
ip authentication mode eigrp 100 md5
ip authentication key-chain eigrp 100 R1chain
network 172.16.1.0 0.0.0.255
accept-lifetime 04:00:00 Jan 1 2006 infinite
send-lifetime 04:00:00 Jan 1 2006 infinite
accept-lifetime 04:00:00 Jan 1 2006 infinite
send-lifetime 04:00:00 Jan 1 2006 infinite
interface FastEthernet0/0
ip address 172.17.2.2 255.255.255.0
ip address 192.168.1.102 255.255.255.224
ip authentication mode eigrp 100 md5
ip authentication key-chain eigrp 100 R2chain
network 172.17.2.0 0.0.0.255
*Jan 21 16:23:30.517: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 192.168.1.102 (Serial0/0/1) is up: new adjacency
R1#show ip eigrp neighbors
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
0 192.168.1.102 Se0/0/1 12 00:03:10 17 2280 0 14
Gateway of last resort is not set
D 172.17.0.0/16 [90/40514560] via 192.168.1.102, 00:02:22, Serial0/0/1
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D 172.16.0.0/16 is a summary, 00:31:31, Null0
C 172.16.1.0/24 is directly connected, FastEthernet0/0
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.96/27 is directly connected, Serial0/0/1
D 192.168.1.0/24 is a summary, 00:31:31, Null0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.17.2.2, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 12/15/16 ms
EIGRP Packets debugging is on
(UPDATE, REQUEST, QUERY, REPLY, HELLO, IPXSAP, PROBE, ACK, STUB, SIAQUERY, SIAREPLY) EIGRP收到一个具有MD5认证的包，key ID为1
*Jan 21 16:38:51.745: EIGRP: received packet with MD5 authentication, key id = 1
*Jan 21 16:38:51.745: EIGRP: Received HELLO on Serial0/0/1 nbr 192.168.1.102
*Jan 21 16:38:51.745: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 pe
EIGRP Packets debugging is on
(UPDATE, REQUEST, QUERY, REPLY, HELLO, IPXSAP, PROBE, ACK, STUB, SIAQUERY,
R2# EIGRP：收到一个具有MD5认证的包，key ID为2
*Jan 21 16:38:38.321: EIGRP: received packet with MD5 authentication, key id = 2
*Jan 21 16:38:38.321: EIGRP: Received HELLO on Serial0/0/1 nbr 192.168.1.101
*Jan 21 16:38:38.321: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 pe
本文转自zcm8483 51CTO博客，原文链接:http://blog.51cto.com/haolun/993181