R2#configure terminal
R2(config)#int f0/1
R2(config-if )# ip address 10.10.10.5 255.255.255.252
R2(config-if )#no shutdown
R2(config)#router eigrp 10
R2(config-router)#no auto-summary
R2(config-router)#network 10.10.10.4 0.0.0.3
R2(config)#key chain cisco123
R2(config-keychain)#key 1
R2(config-keychain-key)#key-string cisco123pass
R2(config-keychain-key)#exit
R2(config)#interface serial f0/1
R2(config-subif)#ip authentication mode eigrp 1 md5
R2(config-subif)#ip authentication key-chain eigrp 10 cisco123
R3#configure terminal
R3(config)#int f0/0
R3(config-if )# ip address 10.10.10.6 255.255.255.252
R3(config-if )#no shutdown
R3(config)#router eigrp 10
R3(config-router)#no auto-summary
R3(config-router)#network 10.10.10.4 0.0.0.3
R3(config)#key chain cisco123
R3(config-keychain)#key 1
R3(config-keychain-key)#key-string cisco123pass
R3(config-keychain-key)#exit
R3(config)#interface serial f0/0
R3(config-subif)#ip authentication mode eigrp 1 md5
R3(config-subif)#ip authentication key-chain eigrp 10 cisco123