MTU handling in 6RD deployments

[Templin, Fred L]

Here's another idea on 6RD MTU. When a 6RD CE router first comes up,
have it ping the BR with a 1520 byte ping. If it gets a reply, don't
advertise an MTU in RA options and set the MTU to the BR to infinity.
If it doesn't get a reply, advertise an MTU of 1480 (or maybe 1472).
No fragmentation and reassembly are permitted.

In the reverse direction, when a 6RD BR forwards a packet to a CE
router that it hasn't ping'd before (or hasn't ping'd recently),
have it ping the CE with a 1520 byte ping. If it gets a reply, set
the MTU to the CE to infinity. If it doesn't get a reply, set the
MTU to 1480 (or maybe 1472). Again, no fragmentation and reassembly.

The only state in the BR then is an MTU value for each CE that it
talks to - in the same way ordinary IPv4 nodes maintain a path MTU
cache for the destinations they talk to. 

Thanks - Fred
fred.l.templin at boeing.com