Host ID.

[gnn at freebsd.org]

I noted that someone mentioned using a network based ID.  Since EUI-64
are unique I would suspect they would be the best source for this on
systems that don't naturally have a hostid concept.  See Appendix A of
RFC 2373 for how to create an EUI-64 Interface Identifier.

The only problem with this approach that I see is that if you remove
that interface (that is it was on a card not on your motherboard) then
it goes away.  Perhaps generating this and storing it, no matter what
the future network configuration of the system is, is the right way to
go.

Best,
George