Problems with OpenBSD dhclient

[Kevin Oberman]

Since switching from the ISC DHCP client to OpenBSD on my laptop, I've
been having some issues with managing my network connection. I'm running
7.0-current built yesterday (kernel and world.)

On a typical day I boot my system on  wired connection with a static
address and gateway. Everything works fine. DHCP is not playing, yet.

When I go to a meeting, I want to switch to the wireless network. In the
past I simply entered 'dhclient wi0' and I was up and running. The
wireless uses DHCP, so dhclient would get the address and gateway along
with DNS servers and instantiate these and I would be connected. The
default route that had been in use previously was replaced with the DHCP
supplied gateway. Switching back was a simple matter of '/etc/rc.d/netif
start fxp0'.

While on the wireless network, I could roam with only brief loss of
connectivity when I moved from one AP to another, but the wireless
system soon "finds" me and I continue on-line with the same address and
gateway. Even my ssh sessions are maintained.

Now life is not so nice with the OpenBSD dhclient.

When I switch to wireless, dhclient no longer replaces the default
route. I need to take down my wired connection and flush routes before
starting dhclient. Not a big deal, but an annoyance.

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.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634