Input, CRC, and Frame errors on 3825 router

Unanswered Question
Aug 14th, 2007

I am getting input, CRC and Frame errors on my serial interfaces. I have 3 T-1's configured with multilink and connect to MPLS.

Attached is an output of the show int.

I am working with our carrier but they say they test clean to the CSU on all three T's. Can anyone let me know any thoughts on what may be causing this? We are getting upwards of 600,000 errors an hour but it does not seem to be affecting our users either with data or our VoIP traffic, and beleive me if we were seeing slowness or issues our users would let us know. Any help would be greatly appreciated.


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Paolo Bevilacqua Tue, 08/14/2007 - 05:21


which exact IOS are you using? The multilink interface is reporting all and any input packets as errors while in fact on 2 or 3 per physical link are errors in 9 minutes.

Also please do "show controllers T1". If any slips, you are probably missing "network-clock" commands.

Unrelated to the above you should configre "no cdp run" and "no fair-queue" under all the interface involved in MLPPP.

thomas.anthony Tue, 08/14/2007 - 06:01

The reliability on ML is 137/255 which is not good

There is lot of framing errors in this interface. A framing error occurs when a packet does not end on an 8-bit byte boundary. Problems that may cause - Noisy serial line or the CSU line clock is incorrectly configured; might one of the clocks is configured for local clocking

burleyman Tue, 08/14/2007 - 06:11

I included the show controllers and the config. It looks like everything is good but check it out...maybe I missed something.


Paolo Bevilacqua Tue, 08/14/2007 - 06:14


Looks like not all the circuit have the same source. Please try to switch networck-clock priority to another circuit.

After that, the slip errors should go away and so the errors on the physical lines. We will then check again the ML interface.

Hope this helps, please rate post if it does!

burleyman Tue, 08/14/2007 - 06:39

I am a little new to the multilink stuff so let me make sure I understand. when you say to switch network-clock priority to another circuit I would change the netowrk-clock-select T1 0/2/0 to like 0/1/0? Will this bring the circuit down?



Paolo Bevilacqua Tue, 08/14/2007 - 07:10

Yes. However it won't bring the circuit down, but you may see that the slips move from a circuit to another.

It is a bit strange because circuits from a same provider via same telco are supposed to have a single clock source and no slips.

[EDIT] OK I understand now that you were using primary clock from a PRI interface. Now because slips are more an issue with voice rather than on data circuits (cause problems especially with faxes) you may find that is better to leave thing as they are and live with the slips on the data circuits.

Paolo Bevilacqua Tue, 08/14/2007 - 06:16

Hi Thomas,

ML is a virtual interface comprising in this case three physical links. The error count must be then the sum of the errors on the individual circuits, thing that is not happening here.


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