r1#show run
Building configuration...

!
key chain private
 key 1   
  key-string 234
!
!
!
interface Loopback0
 ip address 3.3.3.3 255.255.255.0
!
!
interface Serial1/1
 ip address 1.1.1.1 255.255.255.252
 ip rip authentication mode md5
 ip rip authentication key-chain private
 serial restart-delay 0
!
!
router rip
 version 2
 network 1.0.0.0
 network 3.0.0.0
!

r2#show run
Building configuration...

hostname r2
!
!
key chain private
 key 1   
  key-string 234
!
!
interface Loopback0
 ip address 2.2.2.2 255.255.255.0
!
interface Serial1/0
 ip address 1.1.1.2 255.255.255.252
 ip rip authentication mode md5
 ip rip authentication key-chain private
 serial restart-delay 0
!
router rip
 version 2
 network 1.0.0.0
 network 2.0.0.0
!
!