CRC Errors on Router and Swith

Hello everyone:

I am receiving CRC errors on a remote site router's serial port. I
have assumed this to be an issue with our frame-relay provider. But we
are also seeing CRC errors on some of the fast ethernet ports in
switch behind the router. Is this the result of bad packets being
passed from the router to the switch, or could I be looking at two
entirely different problems? Also of note is the fact that on the
switch ports that are showing CRC errors, they are also showing input
errors.

I will check the switch stats for CRC errors later, after we have
resolved the router's issues, but for now I was just trying to
determine if the two are related. Thanks.

 

:I am receiving CRC errors on a remote site router's serial port. I
:have assumed this to be an issue with our frame-relay provider. But we
:are also seeing CRC errors on some of the fast ethernet ports in
:switch behind the router. Is this the result of bad packets being
assed from the router to the switch, or could I be looking at two
:entirely different problems?

I'd say it was two different problems. The packets are being -routed-
at the router, right? That means they would have to be re-written
[to take into account the new destination MAC address]. Even
if the bad packet was not just dropped at the router, the CRC would
be recalculated as the packet is rerouted.

You probably aren't doing transparent bridging on the link? So the
remote end isn't going to be putting in the final MAC address.

 

Yeah their seperate interfaces with their own stats for it.
Basically with CRC, keep watching to see if the CRC values increments.
For your fast ethernet, it could be something as simple as changing your
cable.

For your serial, check with your provider. You could also do a loopback test
to test your cisco cable if in doubt, but nornally its your provider.

 

Try hard setting the speed and duplex on both the switch and router ports.
Sometimes equipment can get crc errors when having to constantly negotiate.

Not sure about the WAN side - bad cable? Timing? With Frame-Relay, you
should get the clocking from the network.

 

Thanks for everyone's advice on this.

The CRCs on the router serial port were a provider issue. Since that
issue has been solved and we are still seeing CRCs on the switch side,
it must be a separate issue. I don't believe it is a cable issue, as
10 ports are showing the errors. It may be a mismatch between the NIC
and switch speed/duplex settings, although I thought that a duplex
mismatch would cause collisions, which I am not seeing.

One final question regarding the input errors I am getting on the
switch. Are the "input" packets coming from the router to the switch
port, from the PC to the switch port, or both?

 

:The CRCs on the router serial port were a provider issue. Since that
:issue has been solved and we are still seeing CRCs on the switch side,
:it must be a separate issue. I don't believe it is a cable issue, as
:10 ports are showing the errors. It may be a mismatch between the NIC
:and switch speed/duplex settings, although I thought that a duplex
:mismatch would cause collisions, which I am not seeing.

What kind of switch is it? Does it happen to be a 2900XL or 3500XL ?
If so, then have you examined the recent Field Notice,
http://www.cisco.com/warp/public/770/fn26174.shtml


:One final question regarding the input errors I am getting on the
:switch. Are the "input" packets coming from the router to the switch
ort, from the PC to the switch port, or both?

You don't give us enough detail to say, but the general principle
that might answer the question is that switches only detect CRC
errors on -received- packets, and they probably drop those packets
before sending them on.

 

Thanks for the info, Walter. It is in fact a 3500XL. I will check out
the field notice.

 

CRC errors on Ethernet interface means bad cable or optioning such as duplex mis-matching issue. If you see CRC error on serial link as well, it could be two different issue on both links (Broadband and baseband).

Sharing Cisco Expertise : www.ipBalance.com

 

CRC errors on router

Dear Friends ,

I have some problem like that. And i can't resolve it. There is a topology that like below:

Router Cisco3800 ------serial link----V35 to E1 converter -------E1 Link -----E1 equipment ------E1---E1 to V35 converter -----Router Cisco3800

And i'm recieving CRC and Input errors on both router. I thought the problem was in clock source. Becouse E1 equipments are having it's clock from another clock source/external/. Now i think i must use router's clock source and configure router as a dce device.

How do you think ?

Ulzii