North American Network Operators Group
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RE: Weird networking issue.

  • From: Daniel Senie
  • Date: Tue Jan 07 18:45:19 2003 
At 05:36 PM 1/7/2003, Mikael Abrahamsson wrote:
On Tue, 7 Jan 2003, Braun, Mike wrote:

> I think we all agree that autonegotiation is evil, and should be avoided
> whenever possible. When you are looking for the root cause of the errors on

I don't agree. I have seen more problems generated by incompetence in
trying to fix duplex/speed, than I have seen problems generated by autoneg
not working properly.

I am always amazed by the fact that very few people out there know that
you have to lock duplex at BOTH ENDS of any given link for it to work
properly.

Generally, in a LAN environment with good quality switches and good
network cards, autoneg works just fine. Yes, with 10/100 meg
fiber/converters converters you should definately lock duplex, but in most
other cases I recommend to leave the duplex setting to auto.

Yes, cisco routers are notoriously bad at doing autoneg, but I blame that
on cisco and not on autoneg. The el cheapo $50 desktop switches seem to
hack autoneg just fine.
Of all the gear I've worked with, from a wide variety of vendors, Cisco is the clear leader in gear that is incapable of successfully doing autonegotiation. I do hope they've improved this in newer products. The all time low point for them has to have been the 2924 switch. Putting a crossover cable between two 2924's yielded invariably BAD results. Now I can forgive engineers for not testing against every brand of router or host out there, but at LEAST test against another copy of the same box you're building. Not even something to blame on a QA engineer... this should have been tested before the box left the engineering benches.

Connections to desktop computers and even servers are often better left set for autonegotiation. As people repatch connections to switches, it's easy to forget to reconfigure the switch.

All that said, it's been my experience that when Cisco routers are involved, you really do have to force the interface settings or tempt fate.