Hi, > -----Original Message----- > From: ipv6-ops-bounces+fred.l.templin=boeing....@lists.cluenet.de > [mailto:ipv6-ops-bounces+fred.l.templin=boeing....@lists.cluenet.de] On > Behalf Of Hannes Frederic Sowa > Sent: Friday, October 18, 2013 12:31 AM > To: Jason Fesler > Cc: IPv6 operators forum > Subject: Re: Caching learned MSS/MTU values > > On Thu, Oct 17, 2013 at 09:05:24AM -0700, Jason Fesler wrote: > > I'm once again considering trying to improve on the test-ipv6.com > PMTUD > > failure detection. Due to limitations on the client side I can't use > raw > > sockets to generate test packets. The client is JavaScript and runs > in a > > browser; all I can do is try fetching urls from multiple locations, > each > > with a different MTU. > > > > I know that the various operating systems tend to cache any PMTUD > issues > > that they can detect; future connections to that destination will use > > smaller packets accordingly. What I can not see to find is an > adequate > > description of what granularity this gets cached with. /128? /64? > Also, I > > the absence of Packet Too Big messages, what does each OS do? > > Linux, too, does cache on /128 basis. In the absence of PTB the > connection > will get stuck. ;)
Right, and we are observing non-negligible cases where PTBs are either not delivered or lost somewhere along the way. That is why there is a growing push for wider deployment of RFC4821 for end systems, and why I am investing my time in developing SEAL for tunnels. Thanks - Fred fred.l.temp...@boeing.com > > Greetings, > > Hannes