AR1
[AR1]int g0/0/0
[AR1-GigabitEthernet0/0/0]ip ad 12.1.1.1 24
[AR1-GigabitEthernet0/0/0]bgp 100
[AR1-bgp]peer 12.1.1.2 as-number 200
[AR1-bgp]
AR2
[AR2]int g0/0/0
[AR2-GigabitEthernet0/0/0]ip ad 12.1.1.2 24
[AR2-GigabitEthernet0/0/0]bgp 200
[AR2-bgp]peer 12.1.1.1 as-number 100