> -----Original Message----- > From: Masataka Ohta [mailto:mo...@necom830.hpcl.titech.ac.jp] > Sent: Tuesday, June 05, 2012 11:36 AM > To: Templin, Fred L; nanog@nanog.org > Subject: Re: IPv6 day and tunnels > > Templin, Fred L wrote: > > >> You don't have to do it with core routers. > > > > Tunnel endpoints can be located either nearer the edges > > or nearer the middle. Tunnel endpoints that are located > > nearer the edges might be able to do reassembly at nominal > > data rates, but there is no assurance of a maximum MRU > > greater than 1500 (which is too small to reassemble a > > 1500+20 packet). Tunnel endpoints that are located nearer > > the middle can be swamped trying to keep up with reassembly > > at high data rates - again, with no MRU assurances. > > As operators know outer fragmentation is used to carry > inner 1500B packets, the proper operation is to have > equipments with large enough MRU. > > As core routers may be good at fragmentation but not > particularly good at reassembly, operators do not > have to insist on using core routers.
I am making a general statement that applies to all tunnels everywhere. For those, specs say that all that is required for MRU is 1500 and not 1500+20. *Unless there is some explicit pre-arrangement between the tunnel endpoints*, the ingress has no way of knowing whether the egress can do better than 1500 outer packet (meaning 1480 inner packet). That is certainly the case for point-to-multipoint "automatic" tunnels as many of these IPv6 transition technologies are. Fred fred.l.temp...@boeing.com > >> I'm afraid you don't understand tunnel operation at all. > > > > I don't? Are you sure? > > See above. > > Masataka Ohta
