-----Original Message----- From: Masataka Ohta [mailto:mohta@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.templin@boeing.com
I'm afraid you don't understand tunnel operation at all.
I don't? Are you sure?
See above.
Masataka Ohta