T-1 input errors and CRC errors

[michael-montgomery]

I am having issues with CRC errors and input errors. I believe this is usually caused by the provider or a bad cable/media. In this case the provider is saying the line tested fine. Any insight on what it could be?

Thanks in advance,

Michael

Router A:

Serial1/1 is up, line protocol is up

Hardware is DSCC4 Serial

Description: T-1 Link to XXXXXX

Internet address is 192.168.40.1/24

MTU 1500 bytes, BW 2048 Kbit, DLY 20000 usec,

reliability 220/255, txload 2/255, rxload 1/255

Encapsulation HDLC, loopback not set

Keepalive set (10 sec)

Last input 00:00:00, output 00:00:01, output hang never

Last clearing of "show interface" counters 00:10:07

Input queue: 0/75/0 (size/max/drops); Total output drops: 11

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/4/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

30 second input rate 5000 bits/sec, 6 packets/sec

30 second output rate 19000 bits/sec, 6 packets/sec

2983 packets input, 497036 bytes, 0 no buffer

Received 70 broadcasts, 0 runts, 0 giants, 0 throttles

2454 input errors, 82 CRC, 2372 frame, 0 overrun, 0 ignored, 0 abort

3744 packets output, 2009767 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

14 carrier transitions

Router B:

Serial0 is up, line protocol is up

Hardware is HD64570

Description: T-1 Link to XXXXX

Internet address is 10.2.5.2/24

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 223/255, load 1/255

Encapsulation HDLC, loopback not set, keepalive set (10 sec)

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0 (size/max/drops); Total output drops: 81

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/3/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

5 minute input rate 12000 bits/sec, 2 packets/sec

5 minute output rate 4000 bits/sec, 3 packets/sec

17495 packets input, 9735370 bytes, 0 no buffer

Received 487 broadcasts, 0 runts, 0 giants, 0 throttles

3689 input errors, 3689 CRC, 15 frame, 0 overrun, 0 ignored, 2685 abort

18513 packets output, 2500400 bytes, 0 underruns

0 output errors, 0 collisions, 7 interface resets

0 output buffer failures, 0 output buffers swapped out

32 carrier transitions

DCD=up DSR=up DTR=up RTS=up CTS=up

[EDWIN.GONZALEZ]

I see you have some carrier transitions and interface resets on router B. You should clear the counters for serial0 on both routers and focus your troubleshooting on router B due to the fact that in has interface resets.

You should create a loopback towards the router and run some ping tests, see if you are still getting interface resets or carrier transitions. If you have still have issues you might have faulty hardware, and if not you should put the pressure on your provider.

I hope this helps.

[scottmac]

How long, and what kind of cable is connecting the router to the NIU / SmmartJack.

If it is a long span (~over ~200 feet) and Cat, then that is a possible source of the problem.

Cat is not really spec for T1, though it is usually acceptable for shorter runs. Spec is "premises cable," which has larger conductors, and individually shielded pair within an overall shielded sheath.

FWIW

Scott

[stephenshaw]

Hi Michael,

you have to go back to the Service Provider and explain to them that you see input errors, CRCs and carrier transitions. Many Telcos test the circuits and say "everything is OK." I would suggest that you ask them to do an end-end test, up to and including the DSU (many Telcos only test circuits to a Communication room and not beyond).

It's unlikely to be a hardware issue - more than likely, as has been suggested, the premises cabling, a bad wall jack, a bad DSU. 99.99% of the time this is a Telco problem, not a router problem.

Good luck,

Steve

[d-buckman]

If your T1 is configured for B8ZF and ESF ask the Telco to peroform an all zeros and all ones test for over 1 minute each (over a minute is key). This failes if there is miss configured equipment on the circuit. If they still insist that the line is OK suggest they give you a loop back toward you router (the one you can get to) and run an extended ping test with 50 - 100 repeates and 1500 byts of payload and use patterns: 0x0000, 0x1111, 0xffff, 0xaaaa, 0xab0f.

I would suggest you 'prove' you DSU/CSU by placing a loopback plug or jack on the line side of your device.

I agree that DSU/CSU units do not often fail but we just found two bad VWIC port modules (made us look bad they did). External Kentrox DSU/CSUs are forever :)

If you prove your DSU/CSU you did your part and the telco can feel free to look futher. Have them give you the loopback starting close to you the work outward to the remote end and see where it fails.

We just went through this on two of our T1 links that were down of 3 days. Glad to be out from under that one.