Can only the 100Mbs part of a 10/100Mbs router fail?

Ken D'Ambrosio kend at xanoptix.com
Wed Dec 8 09:11:02 EST 2004


Hey, Larry!  One thing to contemplate -- though if it had been working 
before, it's not terribly likely to be the problem -- is the fact that 
autonegotiation is an imperfect science.  As an example, at Cisco, we 
always had to peg our server connections at 100MBit on the not-so off 
chance that they'd come up and autonegotiate incorrectly.  So, in a 
nutshell: if there's a way to tell your interface, "Be 100 Mbit!", then 
try it out.

-Ken

Larry Cook wrote:

> I'm having a network problem that appears to be that the 10/100Mbs 
> ports on my router are no longer working at 100Mbs, but are working at 
> 10Mbs. Is it possible that just the 100Mbs part could fail?
>
> Here's my scenario if anyone is interested.  Connected to the router 
> are the following:
>
> Computer #1 w/ 10Mbs NIC
> Computer #2 w/ 10/100Mbs NIC (auto-senses to 100Mbs)
> 100Mbs switch
>
> Computer #1 (10Mbs) works fine, but Computer #2 (100Mbs) and 
> everything behind the 100Mbs switch cannot get to the router.  
> Switching ports on the router and power-cycling the router made no 
> difference.
>
> I put computer #2 (100Mbs) behind the 100Mbs switch and it can get to 
> all computers behind the switch, but not to the router.  So this tells 
> me that the NIC in computer #2 is okay.  It also seems to imply that 
> the 100Mbs switch is okay since computer #2 can talk to another 100Mbs 
> computer behind the switch.
>
> If I replace the 100Mbs switch with a 10Mbs switch, then everything 
> behind it can now get to the router, including computer #2 which 
> auto-senses to 10mbs. But when I move computer #2 back to the router, 
> it auto-senses to 100Mbs and cannot get to the router.
>
> So the only thing that seems to explain my problem is that the 100Mbs 
> part of my router has gone bad, although devices connecting to it are 
> auto-sensing to 100Mbs.  Or is there something that I am overlooking, 
> or something else I should try?
>
> Thanks,
> Larry
>
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