Problems with OpenBSD dhclient

[Bakul Shah]

> > More serious is that I can't roam. When I move between APs, dhclient 
> > exits and I need to manually re-start it. I lose my SSH sessions. Ugh!
> >
> > Worse, I occasionally see my association drop momentarily when I am 
> > simply sitting and typing. Once again, dhclient dies and I must manually 
> > restart it and then re-establish my SSH and recover anything broken when 
> > the connection dropped. This is fairly serious! I don't understand what 
> > causes this, but it is infrequent which makes it hard to catch.
> >
> > It looks like killing dhclient when the interface drops is not a good 
> > idea. At very least, it needs to give a little time for re-association 
> > before dropping the DHCP client.
> 
> I'm experiencing similar or identical problems.  When at the British 
> Library the day before yesterday, slight blips in my association would 
> result in loss of my IP address, requiring manual restarting of dhclient.
> 
> My normal approach for wireless/etc is to settle on a link -- be it wired 
> ethernet or 802.11, and run dhclient on it to get things going.  When 
> done, I'll typically kill off dhclient.  This worked pretty well with the 
> old dhclient setup, but not so well with the new one.  Because I range 
> over a variety of network environments, from adhoc 802.11, wired ethernet, 
> to base station based 802.11, I tend to want to say "do this for now", and 
> have it stick until I move on.  Maybe what I need to change is software 
> configuration -- i.e., devd to re-launch dhclient.  But obviously what I'm 
> doing now isn't working, and results in a pretty poor user experience 
> (blips or roaming and suddenly the network is gone).

To avoid interface flapping perhaps some hysteresis needs to
be introduced in dhclient?  If a link up event occurs within
N seconds of a link down event, ignore them both!  N may need
to be tunable.  Such hysteresis is _not_ needed for
administrative up/down -- when I say `ifconfig ath0 down', I
want it down *now*!

Devd does need to relaunch dhclient (& wpa_supplicant etc.)
on a genuine link up event.