Comcast6.net PMTU broken

[Ryan Rawdon]

From a host behind a 6in4 tunnel a request to www.comcast6.net hangs.  It looks like a PMTU brokenness issue since the connection is established and the request is sent successfully.

Requesting the same page from a host with a 1500B path MTU succeeds.

nova-dhcp-host111:tmp ryan$ wget http://www.comcast6.net
--2012-04-17 17:17:16--  http://www.comcast6.net/
Resolving www.comcast6.net (www.comcast6.net)... 2001:558:1002:4:68:87:29:36, 68.87.29.36
Connecting to www.comcast6.net (www.comcast6.net)|2001:558:1002:4:68:87:29:36|:80... connected.
HTTP request sent, awaiting response... ^C


This only happens with 2001:558:1002:4:68:87:29:36.  2001:558:1004:9:69:242:76:78 (which I've seen listed for www.comcast6.net though I do not see it in DNS currently) does not have this problem