Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Wan Issues - High CRC, aborts, etc

Hello everyone,

We have a monitoring tool here which indicated that one of our routers was experiencing high ping responses.

This router is connected to a router at a seperate office via a T1.

What is the best method of troubelshooting this issue? The ISP has been contacted, the line was brough down and tested and the results we're positive with no issues.

Router 1 = the router which was giving ping issues

Router 2 - router on the other end.

Router 1:

last clearing of counters: 0:28:01

27 input errors

19 crc

1 abort

router 2

last clearing of show interface: 00:29:11

4 input errors

1 crc

3 frame

router 2 had the following issues before the counter was reset:

last clearing of show interface counters 7w2d

14235 input errors

6428 crc

547 aborts

277 interface resets

Does anyone see any issues here? How can you determine what is causing the errors?


  • WAN Routing and Switching
Hall of Fame Super Gold

Re: Wan Issues - High CRC, aborts, etc


Ask the carrier to execute a BERT test for at least 2hr, and be try to be present to observe the results with your own eyes. That might have not be done and they just executed a "continuity" test.

Then with a succession of loopbacks hopefully they can get to trace the faulty portion. It may even be the local cabling.

New Member

Re: Wan Issues - High CRC, aborts, etc

Thanks, I can try that.

When you refer to the cabling, are you referring to the csu.dsu cabling? Do you think the prelude csu/dsu box can be at fault as well and possibly need a replacement? I don't see any errors on the box itself.

Is there anything which I can do locally to try and test and diagnose...


Hall of Fame Super Gold

Re: Wan Issues - High CRC, aborts, etc


yes also dsu/csu cabling should be checked and redone as necessary. What you can do to test are various types of loopback, what router interface do you have ?

New Member

Re: Wan Issues - High CRC, aborts, etc


How do I perform the loopback tests?

What do you mean by the type of router interface? Are you referring to the model? It's a cisco 2500.


Re: Wan Issues - High CRC, aborts, etc


You have basically two choice to make BER test.

1. Put a hardware loopback on the DTU port.

2. Ask telco to put a software loopback on the DTU

The only question is in which direction do you want to make the testing.

In respect to the interface type it is most probably X.21, V.35 RS-232

You can easily identify it by inspőecting your cable.

If you want to do the loopback test you have to have BER tester to be connected to the DTU. This device is sending bit stream on the transmit and hears on the receive and if the sent and received bits are the same then there are no error. If you haven't this kind of box let's ask the telco to ride to your site and make the test from your end (in this case the loopback should be set on the other end of the circuit).

Hope it clears,


New Member

Re: Wan Issues - High CRC, aborts, etc

Thanks a lot for the response. We're running a V.35 cable here. I may have to contact them back then b/c we don't have the hardware to do the BER testing.

We had the same issue last night. It's usually at a specific time in the morning when no traffic is traversing (or shouldn't be)

I may have to setup a syslog server to determine the packet flow at that time.

Does anyone know if a syslog server can be setup on a windows machine, or does it have to be setup on a linux/unix box? Anyone have any links or instructions on the setup of a syslog server?

Thank again

Re: Wan Issues - High CRC, aborts, etc

You can setup a syslog on windows. Try this kiwi's sylog daemon. it is free up to 5 clients

New Member

Re: Wan Issues - High CRC, aborts, etc

I agree with others about the hard loop. Often times, the carrier will loop to the NIU, and depending on your scenario, will leave an extended demarc untested.

Based on what I've read, and since this looks like a p2p, I would suggest looking at the clocking on the controller. You would need to check with the SP, but from my experience clocking isn't provided on a p2p. You'll need one controller set as line/network, and one as internal.

I've seen quite a few crc/frame error problems resolved with clocking.

Hall of Fame Super Gold

Re: Wan Issues - High CRC, aborts, etc

[edited - pls ignore]