Hi Ole, > -----Original Message----- > From: otroan@xxxxxxxxxxxxx [mailto:otroan@xxxxxxxxxxxxx] > Sent: Tuesday, February 14, 2017 11:17 AM > To: Templin, Fred L <Fred.L.Templin@xxxxxxxxxx> > Cc: Stewart Bryant <stewart.bryant@xxxxxxxxx>; Brian E Carpenter <brian.e.carpenter@xxxxxxxxx>; gen-art@xxxxxxxx; 6man WG > <ipv6@xxxxxxxx>; ietf@xxxxxxxx; draft-ietf-6man-rfc1981bis.all@xxxxxxxx > Subject: Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04 > > Fred, > > >> Yes, but sending at 1280 does not work for IP tunnels. The whole purpose of the minimum MTU was to give space for tunnel > headers > >> (1500-1280). > > > > But, if non-tunnel links set a 1280 MTU which is perfectly OK with the standard then > > there is no space for headers. Given the issues with classical PMTUD then (plus the > > non-applicability of RFC4821 for tunnels) the only solution for tunnels is fragmentation. > > I'll let Joe step in if he wants to. > > You are correct. "Does not work for IP tunnels without fragmenting the outer header" is what I should have written. > Of course it appears IPv6 fragments have a order of magnitude higher drop probability than ICMP PMTUD messages. Right. Depending on the encapsulation, however, fragmentation might occur as some mid-layer between the outer and inner IP headers. For example, a UDP encapsulation that includes its own fragmentation control fields. In that way, the network would only see UDP/IP packets - it would not see IPv6 fragments. GUE is an example UDP encapsulation that include its own fragmentation control fields: https://datatracker.ietf.org/doc/draft-herbert-gue-extensions/ > Pick your poison. As far as RFC 2473 is concerned, you are right. Other encapsulations that can do the fragmentation at a mid-layer between the inner and outer IP headers should be OK. Thanks - Fred > Best regards, > Ole