Hi Tore, > -----Original Message----- > From: Tore Anderson [mailto:[email protected]] > Sent: Tuesday, January 07, 2014 9:57 AM > To: Templin, Fred L; IPv6 Ops list > Subject: Re: MTU handling in 6RD deployments > > * Templin, Fred L > > > 6RD could use SEAL the same as any tunneling technology. SEAL makes > > sure that packets up to 1500 get through no matter what, and lets > > bigger packets through (as long as they fit the first-hop MTU) with > > the expectation that hosts sending the bigger packets know what they > > are doing. It works as follows: > > > > - tunnel ingress pings the egress with a 1500 byte ping > > - if the ping succeeds, the path MTU is big enough to > > accommodate 1500s w/o fragmentation > > - if the ping fails, use fragmentation/reassembly to > > accommodate 1500 and smaller > > - end result - IPv6 hosts always see an MTU of at least 1500 > > In order for the BR to support reassembly it must maintain state. That's > going to have a very negative impact on its scaling properties...
A couple of things about this. First, reassembly is used only for packets in the range of 1280-1500 bytes (smaller and larger packets are passed w/o fragmentation). Second (and more importantly) reassembly is not needed for packets of any size if the path can pass a 1500 byte ping packet. So (as Ole said a few messages back) if the 6rd domain MTU can be made to be >=1520 the fragmentation and reassembly process is suppressed and only whole packets are transmitted. Thanks - Fred [email protected] > Tore
