In message <385F3D8B.F46FE3AD@augustsson.net> Lennart Augustsson writes:
: Does it allow you to have, say, an open TCP connection, unplug one
: card, plug in another (with a different IP number) and continue
: using the connection?

If it has a different IP number, there is no way possible for the
connection to continue since one end of the 4-tuple tcp address is
gone...  The TCP protocol on the remove side would issue a RST since
the remote site doesn't have a connection established to the new IP
address.

I was able to ssh to a remove machine, remove and reinsert the card
and the connection survived.  dhclient survives and gets a new IP
address if I need it.  When the card is removed, the driver's detach
routine calls if_detach to obliterate the interface.

I suspect that swapping cards would still work, so long as it gets the 
same IP address.  My dhcp world is such right now that I'm getting two 
different IP addresses for the two different cards (one is an linksys
and uses FreeBSD ed driver, the other is 3c589D and uses ep).

I think the network stacks are congruent enough that porting this
wouldn't be too hard.  It has no dependencies on the driver framework,
other than to be called from drivers detach routines from time to
time.

Warner