When I turn on PMTU discovery, I get lots of clutter:

Destination        Gateway            Flags     Refs     Use    Mtu  Interface
pm300-36.tr.net-li near-gw.cygnus.com UGHD        0      247   1006  de0
pm300-39.tr.net-li near-gw.cygnus.com UGHD        0      224   1006  de0
pm301-14.tr.net-li near-gw.cygnus.com UGHD        1     2148   1006  de0
pm301-29.tr.net-li near-gw.cygnus.com UGHD        0     4226   1006  de0
pm301-46.tr.net-li near-gw.cygnus.com UGHD        0      405   1006  de0

Note that only one of these hosts is really in use.  Shouldn't
the others expire when the reference count reaches zero, or
at least after a timeout after the ref count reaches zero?

--Michael