Different Junos OS versions allow the configuration of identical source and destination IP addresses on GRE tunnels. Junos OS version 11.4 does not display any warning or error when performing commit check; later versions such as 12.3, 14.2, 13.3 display a notice that the configuration check-out failed. This article describes the problem and recommends using different source and destination IP addresses on GRE tunnels.
Configuring the same IP addresses for source and destination on a GRE tunnel results in the following error:
user1@router# show interfaces gr-0/0/0 |display set
set interfaces gr-0/0/0 unit 0 tunnel source 10.0.0.1
set interfaces gr-0/0/0 unit 0 tunnel destination 126.96.36.199
set interfaces gr-0/0/0 unit 1 tunnel source 10.0.0.1 << same as tunnel 0
set interfaces gr-0/0/0 unit 1 tunnel destination 188.8.131.52 << same as tunnel 1
user1@router# commit check
[edit interfaces gr-0/0/0 unit 1]
Duplicate source and destinations should not be used regardless of the error message appearing. Source and destination addresses of a tunnel cannot both be the same as those of another tunnel on the device.
error: configuration check-out failed
You can also configure GRE Keepalives.