IPv6 PMTUD and OS-X

Franck Martin franck at genius.com
Fri Aug 20 16:27:03 CDT 2010


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. There are IPv6 web site that I cannot browse until I lower the MTU to 1400. My Linux desktop in similar config works fine... 
With tracepath6, I see one end of the tunnel tells me MTU should be 1280, that's using linux tools. 

On mac, tracepath6 does not seem to exist, and I don't know what tool to use... I have seen scamper, but no binary... 

I have used wireshark (on mac) to detect the PTB packet, but don't see it either... I have not compared with my linux box... 

I'm doing this testing on the side, slowly because it is fun to try to understand what's wrong here... and I wonder if others have had similar issues... 

May be not fully on topic, but to bring it back to topic see this presentation: 
http://www.ripe.net/ripe/meetings/ripe-60/presentations/Stasiewicz-Measurements_of_IPv6_Path_MTU_Discovery_Behaviour.pdf 

Which states the PMTUD failure rate on IPv6 is about 1.9% 



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