On Fri, 26 Jan 2007 13:59:19 +0100
Pavel Cahyna <pavel@NetBSD.org> wrote:

> On Thu, Jan 25, 2007 at 08:36:53PM -0500, Steven M. Bellovin wrote:
> > I may have another clue...
> > 
> > I noticed that I only seemed to feel the problem when I was using my
> > laptop directly; as it happens, I generally do that when using
> > either 802.11 or EVDO.  By contrast, when I've logged into it
> > remotely, I'm almost always on a wired net.
> > 
> > I tried running for a while with no network connectivity, i.e.,
> > with no EVDO card inserted and with ath0 ifconfig'ed down.  The
> > problem still occurred.  On a whim, I disabled wm0 -- and the
> > problem stopped....
> 
> Do the interface flags for wm fluctuate often? For example, by turning
> PROMISC on and off?
> 
> Could you show your dmesg?
> 

I believe you were on the right track.  I think I understand the
problem now.

I had changed my dhclient.conf file to include


	interface "wm0" {
	       media "media autoselect";
	}

That meant that any time I was using wireless or EVDO, dhclient was
still trying to acquire a wired lease.  This in turn meant constant
ifconfigs to change the media type, and neither dhclient nor the driver
noticed that these were the options already in effect.  Furthermore,
doing this sort of change seems to grab the whole machine briefly,
though I haven't figured out quite why.

I've deleted that line.  I may put it in my /etc/apm/resume file.
(This being a wm, it has problems with speed negotiation, and I move
between 100M and GigE networks.)

		--Steve Bellovin, http://www.cs.columbia.edu/~smb