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Need help troubleshooting CRC errors

Some of our older remote sites are connected via ATM. Two or three T1s come into an Cisco 8510, and from there a 155mbps OC3 connection over fiber to a 3640 router. Lately, I've been noticing that pretty much every one of them is showing what I think is a rather high receive error count on the 3640 end of the OC3 connection, and it all seems to be CRC errors. Not much of any errors are showing up on the 8510 end of the OC3 connection. For example, one site yesterday late afternoon showed 63, 763 receive errors for the day. Several others were in the

20Ks. I'm not really certain what the cause might be, or where to start. Can anyone help?

Thanks!

Reply to
pfisterfarm
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The transmit fiber on the 8510 is probably having an issue. Since this is OC3, I'm going to assume that the fiber has been in place for quite a long time. Could be as simple as some dust and you just need to use a can of air to clean everything out, or it could be a bad connector and you need to reterminate one or both ends. The glues that were used way back did not hold up over time and would eventually fail. Could also be faulty optics on either the transmit or recieve. You can try swapping the trasmit and receive on both ends and if you see the errors on the 8510, then you definately have a fiber problem. If you still see errors on the 3640, then its probably with the transmit optics on the 8510.

Reply to
Thrill5

I have a little more detail about the problem now:

'show atm pvc x/y' shows:

CrcErrors: 69402, SarTimeOuts: 2, OverSizedSDUs: 0, LengthViolation:

69294, CPIErrors: 0

Also, the router side shows, on 'show int':

MTU 1500 bytes, sub MTU 1500, BW 155000 Kbit, DLY 80 usec,

router side, on 'show atm int atm':

Max. Datagram Size: 1558

8510 switch side, on 'show int':

MTU 4470 bytes, sub MTU 4470, BW 155520 Kbit, DLY 0 usec,

Would this be a problem?

Reply to
pfisterfarm

If you look at the outputs from 'sh controller T1 X/Y' on the 3600 series, do you see FEBE (Far End Bit Error), LCV (Line Code Violations) or PCV (Path Code Violations) counters increment ? If it's Path code, I'd point my finger towards the 8510, or the transport network, If it's Line code, then it's most likely local (to the 3600) cabling.

Have a read over this doc:

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it'll outline what the counters on 'sh controller t1' mean, then you can step it up to this doc (Mostly specific to the PA-A3, however the counters mean the same on every controller, they're just might be called something else) :
formatting link
Keep an eye on which counters are incrementing, and at which rate (hint, use 'ter exe pr t' to put a timestamp at the top of every show command).

Regards, Ruairi

Reply to
Ruairi Carroll

Yes the MTU could mismatch could be the problem. Set the MTU on the 8510 to

1500 using the command "mtu 1500" on the sub interface.

Reply to
Thrill5

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