[c-nsp] Cisco 1841 Router CRC errors

[Tom Storey]

On 18/12/2007, at 7:42 AM, Paul - Talk Talk wrote:

> We have upgrade our lease line from 4mb copper to 10mb fibre which  
> meant we
> had to change our router.
>
> The old router was a Cisco 2620 and the new Router is a Cisco 1841.
>
>
>
> Between the Cisco Router and our Cisco 3550 layer three switch is a
> bandwidth management box, which is an Allot NetEnforcer AC-402.
>
>
>
> On the old the old set-up using the Cisco 2620 everything worked fine.
>
>
>
> On the new set-up with the Cisco 1841 we are seeing a lot of CRC  
> errors
> until the whole thing falls over.
>
>
>
>> From our side nothing has changed except the router which was  
>> supplied by
> the ISP.
>
>
>
> We did find out that the FE0/0 interface on the Cisco 1841 was set  
> to auto,
> but this has now been set to Full Duplex 100mb which matches the Allot
> NetEnforcer.
>
>
>
> Taking the NetEnforcer out and connecting to the Cisco 1841 directly  
> to the
> Cisco 3550 stops the errors, but as said before switching back to  
> the Cisco
> 2620 also stops the errors.
>
>
>
> Any help would be appreciated.
>
>
>
> Kind Regards
>
> Paul Stainton
>
>
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On one particular PC I have cannot auto negotiate and cannot be set to  
100/full without producing errors. I have to run it in 100 half. At  
least this one is only a PC. Its got a Broadcom NIC.

My suggestion would be, if you can spare two ports on the switch, to  
create a VLAN and stick the two interfaces that would normally connect  
directly to each other into that VLAN. Otherwise, try different cables  
between the two, set the port to 100/half, and try different  
interfaces if you can.

I may have other issues with the PC above, such as a dodgy cable. I  
havnt gone so far to test that out yet as its bandwidth requirements  
are low, 100/half does just fine.