I was seeing some 'TTL Expired in Transit' on our network devices. This can indicate a routing loop so I took it seriously. Not finding any routing loops, I performed a packet capture which showed that lots of our phone handsets (Avaya 9608's) are regularly sending out ping's to the Avaya PBX with TTL's starting at 1 (which then expire at the first hop), and increasing by 1 until they reach their destination.
This was why I was seeing lots of TTL expired messages when I enabled ICMP debugging on our network devices.
We have had reports of calls dropping, so I was wondering if this mapping out of the number of hops to the PBX is something all 9608's do on a regular basis or if it is a symptom of a problem I am yet to uncover?
