Solaris 2.x sets the don't fragment bit on all packets it send
as part of MTU path discovery. The Solaris 2.x implementation
is RFC compliant, but the MTU path discovery protocol will
fail when there are broken routers in the path.
Typical symptom is not being able to connect from a
Solaris 2.x hosts but having no trouble from other hosts or
being able to start a TCP/IP connection but not move any
significant amount of data.
/usr/sbin/ndd -set /dev/ip ip_path_mtu_discovery 0
(See also 5.19)