Subject: Re: Regarding 802.3u NWAY autonegotiation, hubs, media, etc.
To: Jason Thorpe <>
From: Charles M. Hannum <>
List: tech-net
Date: 12/09/1999 17:18:41
Jason Thorpe <> writes:

> 	(1) Change the way we hard-wire media:
> 		(a) If ANER_LPAN, set ANAR_x to the appropriate
> 		    bits corresponding to our media, and set
> 		    Our link partner is NWAY-capable, so advertise
> 		    only the media we want to switch to, and begin
> 		    NWAY.  This should cause both ends to resolve
> 		    to the specific media we want.
> 		(b) If not ANER_LPAN, set BMCR_x to the appropriate
> 		    bits corresponding to our media.

I have two concerns about this:

* How do you get ANER_LPAN at startup time (e.g. if I do `ifconfig
  tlp0 inet ... media 10baseT up' to *initialize* the interface)?
  Send a FLP and wait 5 seconds?

* If you have two NetBSD machines connected via a cross-over cable,
  and both doing NWay, then switching them one at a time to a static
  configuration will not work.  Both sides will still be doing NWay
  when you're done.  I think even rebooting one side will still cause
  them both to be doing NWay.  There should be some way of saying `No,
  don't f*cking use NWay, damn it.'

It also seems like way too much magic.

At the very least, this should be documented clearly, and the kernel
should tell me somewhere that it's decided to do NWay all the time, so
I have a prayer of figuring out what happened when it does fall over.

Perhaps the right thing to do is your point #1, but only long enough
to send a FLP to inform the other side (or for 5 seconds?), and then
switch to Parallel Detection.