On 17/02/2017 04:59, Stewart Bryant wrote: > > > On 14/02/2017 23:00, Templin, Fred L wrote: >> Unless there is operational assurance of >> some size X>1280, however, tunnels have to use fragmentation to >> guarantee that - at a minimum - packets up to 1280 will get through. > > In that case there really needs to be a note about MPLS. > > You can fragment into an IP tunnel, but not an MPLS tunnel, because you > cannot fragment the payload as you can in IPv4 and you cannot fragment MPLS. I'm confused. A tunnel end point that accepts IPv6 packets MUST accept packets of 1280 bytes (or shorter) and MUST emit them. How it gets them through the tunnel is irrelevant - if it's an ATM tunnel it has to chop them into 48 byte fragments and re-assemble them at the other end - if it's an avian carrier tunnel it might have to use several pigeons per packet*. None of this matters to the IPv6 nodes concerned; the physical MTU of the tunnel technology is irrelevant except to the tunnel end points. Brian *In RFC 6214, we didn't consider this, but we should have.