Bug 35017

See also 
http://docs.freebsd.org/cgi/getmsg.cgi?fetch=167189+0+current/freebsd-net

During the setup of an IPv6 over IPv4 tunnel, the freenet port uses
the statement: "route add -inet6 default -interface gif0"

When sending TCP traffic over this tunnel, the first few packets
get send without problems until my host starts sending out CMP6
neighbor solicitation requests. From that moment on, my host doesn't
send any packet anymore for this TCP session. New TCP sessions can
be start without problems (but experience the same problems), ICMP6
packets of other sessions keep flowing without interruption. It's
only this TCP session which is hanging.

I've posted a message about this in -hackers and -net and got two
groups of answers: yes I have the same problem and no I don't have
this problem anymore since I've changed to a different IPv6 provider.

When comparing what was going different with different providers,
I saw they were issueing the "route add -inet6 default ipaddress"
Statement instead of the "route add -inet6 default -interface ..."
statement. When using this statement in the scripts of freenet6 my
tunnels stayed up without problems.

I have informed the people from freenet6.net about this, I have
submitted a patch for the net/freenet6 port. But the real problem
lies somewhere in the way FreeBSD 4.5 is looking through its
routing-table.

Fix: 

Unfortunatly I'm not skilled enough to fix what is going wrong here...
How-To-Repeat: 
Install net/freenet6 version 0.9.5 and setup a tcp-session towards
an IPv6 enabled host.