拓扑图：
配置：
R1：
key chain ccna
key 1
key-string cisco
call rsvp-sync
!
interface Loopback1
ip address 1.1.1.1 255.255.255.0
!
interface Serial1/0
ip address 12.1.1.1 255.255.255.0
ip authentication mode eigrp 1 md5
ip authentication key-chain eigrp 1 ccna
serial restart-delay 0
!
router eigrp 1
network 1.0.0.0
network 12.0.0.0
no auto-summary
R2：
key chain ccna
key 1
key-string cisco
call rsvp-sync
!
interface Serial1/0
ip address 12.1.1.2 255.255.255.0
ip authentication mode eigrp 1 md5
ip authentication key-chain eigrp 1 ccna
serial restart-delay 0
!
interface Serial1/1
ip address 23.1.1.1 255.255.255.0
ip authentication mode eigrp 1 md5
ip authentication key-chain eigrp 1 ccna
serial restart-delay 0
!
router eigrp 1
network 12.0.0.0
network 23.0.0.0
no auto-summary
!
R3：
key chain ccna
key 1
key-string ccie
call rsvp-sync
!
interface Loopback1
ip address 3.3.3.3 255.255.255.0
!
interface Serial1/0
ip address 23.1.1.2 255.255.255.0
ip authentication mode eigrp 1 md5
ip authentication key-chain eigrp 1 ccna
serial restart-delay 0
!
router eigrp 1
network 3.0.0.0
network 23.0.0.0
no auto-summary
!
说明
1.R1与R2验证是成功的，因为他们的key ID和密钥都是相同的
2.R2和R3验证不成功，因为他们钥匙链的密钥不相同
DUAL-5-NBRCHANGE: IP-EIGRP 1: Neighbor 23.1.1.1 (Serial1/0) is down: Auth failure
R3#debug eigrp packet
EIGRP: key id = 1, authentication mismatch
EIGRP: Serial1/0: ignored packet from 23.1.1.1, opcode = 5 (invalid authentication)
