Hi Ragnar, > -----Original Message----- > From: Anfinsen, Ragnar [mailto:ragnar.anfin...@altibox.no] > Sent: Thursday, January 09, 2014 11:36 AM > To: Templin, Fred L; S.P.Zeidler > Cc: IPv6 Ops list > Subject: Re: MTU handling in 6RD deployments > > On 09.01.14 17:36, "Templin, Fred L" <fred.l.temp...@boeing.com> wrote: > > > >But, in some environments we might not want the 6rd BRs to suffer from > >sustained fragmentation and reassembly so a responsible network operator > >would fix their IPv4 link MTUs to 1520+. If they can't do that and the > >load on the 6rd BR appears too great, then MSS clamping and a degenerate > >IPv6 MTU reported to the IPv6 hosts is the only option. > > The problem with your statement
Where do you see a problem with my statement - it agrees with what you said below: > is that many L3 access networks do not > support MTU greater than 1500 on the access port. And if the RA MTU is set > to 1480, you would not see any problems at all. However, there are some > retail routers which do not set the MTU to 1480 when using a 6rd tunnel. > In these cases adjusting the MSS if a good and efficient way of correcting > that problem. Our experience so far is that MSS-clamping does not have any > additional CPU load compared to not do it. I don't doubt that your experience is valid for the environment you are working in. What I am saying is that there may be many environments where setting IPv4 link MTUs to 1520+ is a viable alternative and then the hosts can see a full 1500+ MTU w/o ICMPs. SEAL detects when such favorable conditions exist and uses limited fragmentation/reassembly only when they don't. Or, if fragmentation/reassembly is deemed unacceptable for the environment, then clamp the MSS. Thanks - Fred fred.l.temp...@boeing.com > /Ragnar >