IPv6 day and tunnels

Tue Jun 5 19:41:47 UTC 2012

Templin, Fred L wrote:

> I am making a general statement that applies to all tunnels
> everywhere.

General statement?

Even though you assume tunnel MTU 1500B and tunnel overhead 20B?

> For those, specs say that all that is required
> for MRU is 1500 and not 1500+20.

That is a requirement for hosts with Ethernet interface, which
is, by no means, general and has nothing to do with tunnels.

For the general argument on tunnels, see, for example,
RFC2473 "Generic Packet Tunneling in IPv6", where there
is no requirement of 1500.

Note that the RFC uses outer fragmentation:

        (b)  if the original IPv6 packet is equal or  smaller  than  the
             IPv6 minimum link MTU, the tunnel entry-point node
             encapsulates the original packet, and subsequently
             fragments the resulting IPv6 tunnel packet into IPv6
             fragments that do not exceed the Path MTU to the tunnel
             exit-point.

					Masataka Ohta