Today a customer asked me to add a peer via the Lonap peering LAN to their border routers. Normally a trivial operation as we, like everybody else use a peer-group arrangement, but on this occasion it would not accept the config:
router1(config)#router bgp 8401 router1(config-router)#neighbor 18.104.22.168 remote-as 12345 % Create the peer-group first
After some Googling I found that there is a ‘bug’ in the IOS which means that if somebody tries to configure an invalid ip address (i.e. a typo), then until the device is reloaded, no more peers can be added. Although i found i could add peers with different ip addresses altogether? In the end I used the workaround command:
no parser cache
Which solved the issue.