[c-nsp] Negotiation problem with Catalyst 2950 and Cisco 2821

[Ted Mittelstaedt]

>-----Original Message-----
>From: Jay Hennigan [mailto:jay at west.net]
>Sent: Friday, December 02, 2005 9:40 PM
>To: Ted Mittelstaedt
>Cc: cisco-nsp at puck.nether.net
>Subject: Re: [c-nsp] Negotiation problem with Catalyst 2950 and Cisco
>2821
>
>
>Ted Mittelstaedt wrote:
>
>>Hi All,
>>
>>  I hae a stock 2821 router with 2 gig E ports on the inside,
>>and 2 load-balanced t1's going to the Internet, running NAT.
>>IOS version is 12.4.5
>>
>>  I have several 2950's don't know what version of firmware
>>(probably old).
>>
>>  I plug the 2821 into the 2950s and set the 2821 and 2950 to 
>>autonegotiate speed and duplex.
>>
>>  The 2821 negotiates to 10 base T half duplex.  Users
>>report problems with intermittent disconnects and slowness
>>when surfing the web, etc.
>>
>>  I go to Goodwill, no less, and purchase a 10 year old 8
>>port dumb hub, 10BaseT only.  Not a switch.  Cost is $7.99
>>
>>  I insert this hub between the 2821 and the Catalyst 2950.
>>
>>  Problems of disconnects and slowness go away.
>>
>> Speculation, anyone?
>>  
>>
>Duplex negotiation mismatch.  Fairly common.  Cisco has used a
>variety of chipsets for ethernet ports over the years.  Many of
>them seem to not play well with others.  You're probably seeing
>a lot of collisions and runt errors on the interfaces.  Seeing
>as the layer 1 connection between these devices isn't likely to
>change, why not set both devices for the best throughput, in
>this case 100 mbits/s, full-duplex? 
>

Hard-coding 2 autonegotiation interfaces that are connected to
each other often causes errors.  It only works some of the
time.

>Then you can donate that extra 10-base-T hub to the Goodwill.
>

Never, I always carry one of these nowadays, specifically for
isolating these kinds of problems.

Ted