This page describes some IPv6-related issues.
"IPv6: sending pkt_too_big to self"
This is a message that sometimes appears in syslog on a machine with LinuxKernel2.6.
Apparently this is caused by path MTU discovery for paths that use a local tunnel, such as 6to4 or IPSec. This is really just a debugging statement rather than an error, and can be safely ignored.