Hello, Several months ago, there was discussion on the list regarding IP tunnel maximum transmission unit (MTU). Since that time, it has been brought to my attention by members of my company's network operations staff that tunnel MTU is a very real problem they need to cope with on a daily basis - especially with the growing need to depend on both tunnels and tunnels-within-tunnels to track mobile devices. Since tunnels always reduce the effective MTU seen by data packets due to the encapsulation overhead, the only two ways to accommodate the tunnel MTU is either through the use of path MTU discovery or through fragmentation and reassembly. Unfortunately, both are known to be problematic in a non-trivial number of cases. The discussions on NANOG from back in the June timeframe resulted in "Operational Issues with Tunnel Maximum transmission Unit": https://datatracker.ietf.org/doc/draft-generic-v6ops-tunmtu/ I would like to ask this group to now give this document a look and post your comments/thoughts/experiences. For example, has the tunnel MTU problem crept into daily operational considerations to the point that we should now at least be documenting it and preferably trying to do something about it? From talking to our staff, I believe the answer is yes but it would be good to have confirmation from others. Thanks in advance for your thoughts, Fred fred.l.templin@boeing.com