21 Aug
2010
21 Aug
'10
5:42 a.m.
On 2010-08-21 09:18, bmanning@vacation.karoshi.com wrote: > On Fri, Aug 20, 2010 at 11:34:23PM +0200, Jeroen Massar wrote: >> On 2010-08-20 23:27, Franck Martin wrote: >>> I'm trying to debug a pesky PMTUD issue with IPv6 on Mac OS-X 10.6. >>> >>> It happens only from home, on wireless, when connected to a mac aiport >>> that does an automatic tunnel (teredo) to IPv6 backbone. >> >> Welcome to the great world of Teredo/6to4 where the endpoints/relays of >> the tunnel are anycasted in both IPv4 and IPv6 and thus can be quite >> difficult to debug, it can be done but requires quite a lot of vision in >> the network on both IPv4 and which will be generally near impossible. >> >>> There are IPv6 web site that I cannot browse until I lower the MTU to >> 1400. >> >> Why don't you just do 1280 which is the default? >> >> Do also note that you have two levels of PMTU, the IPv6 one and the IPv4 >> one. If you configure your MTU of the tunnel incorrectly compared to the >> relay that you are using you will not see the PMTU's coming through >> either or they might not accept your large packets. >> >> Both MTUs can be broken due to folks filtering ICMP which is generally a >> bad thing to do. >> >> Greets, >> Jeroen > > > or - if you are tunneled more than once, you might be ultra conservative > and drop your MTU to 1220 - that should weed out the edge cases where even 1280 > is too large. 1220? I am pretty sure the minimal IPv6 MTU is 1280 and that below it fragmentation should be handled by the medium that transports packets smaller than that.... Can you enlighten me Bill? :) Greets, Jeroen