MTU handling in 6RD deployments

[Tore Anderson]

* Templin, Fred L

> 6RD could use SEAL the same as any tunneling technology. SEAL makes
> sure that packets up to 1500 get through no matter what, and lets
> bigger packets through (as long as they fit the first-hop MTU) with
> the expectation that hosts sending the bigger packets know what they
> are doing. It works as follows:
> 
>   - tunnel ingress pings the egress with a 1500 byte ping
>   - if the ping succeeds, the path MTU is big enough to
>     accommodate 1500s w/o fragmentation
>   - if the ping fails, use fragmentation/reassembly to
>     accommodate 1500 and smaller
>   - end result - IPv6 hosts always see an MTU of at least 1500

In order for the BR to support reassembly it must maintain state. That's
going to have a very negative impact on its scaling properties...

Tore