CRC errors on serial links

[lgontarsk]

Hi, I just want to make sure... CRC errors are always exactly that on serials? We've been arguing with the carrier about the CRC errors on our links.... Are CRCs are always bad facilities/noise on the links? Is there anything else for us to check out other than to go thru our carrier on this? Below are some show commands.

please see the attachments...

thanks!

interface Serial1/0

description DS3 to r002-sea-crx s1/0 - Sprint PL# 484164

bandwidth 45000

ip address 172.31.193.38 255.255.255.252

dsu bandwidth 44210

scramble

end

interface Serial2/0

description DS3 to r001-atl-crx s6/0 - MCI/VZB DS3 Ckt ID: W0P76319

bandwidth 45000

ip address 172.31.193.162 255.255.255.252

dsu bandwidth 44210

end

Serial1/0 is up, line protocol is up

Internet address is 172.31.193.38/30

Serial2/0 is up, line protocol is up

Internet address is 172.31.193.162/30

Serial1/0 is up, line protocol is up

Hardware is DSXPNM Serial

Description: DS3 to r002-sea-crx s1/0 - Sprint PL# 484164

Internet address is 172.31.193.38/30

MTU 4470 bytes, BW 45000 Kbit, DLY 200 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation HDLC, crc 16, loopback not set

Keepalive set (10 sec)

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

Last clearing of "show interface" counters 1w6d

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

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 147000 bits/sec, 47 packets/sec

5 minute output rate 3000 bits/sec, 2 packets/sec

40897343 packets input, 2131993825 bytes, 0 no buffer

Received 134668 broadcasts, 0 runts, 0 giants, 0 throttles

4932 input errors, 4930 CRC, 505 frame, 1529 overrun, 0 ignored, 577 abort

21748430 packets output, 1278439926 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

DSU mode 0, bandwidth 44210, real bandwidth 44210, scramble 1

Serial1/0 buffers, 1504 bytes (total 128, permanent 128):

0 in free list (0 min, 128 max allowed)

128 hits, 0 fallbacks

128 max cache size, 64 in cache

47224495 hits in cache, 0 misses in cache

[patrickvanham · Accepted solution]

The errors seem to go both ways on serial 1 and are a mix of errors, both ways. As your ISP to provide a loop at demarc at both istes and check if the errors still happen. If you're error-free then their line is bad.

The second serial (serial 2 to serial 6) shows serial 6 clean and serial 2 abort. Ask for a loop at the demarc closesest to the router where serial 2 is connected towards the remote en and check for errors, and ask to move one step closer until they disappear.

[lgontarsk]

Thank you both for the excellent responses.

LisaG

[srimural · Accepted solution]

Hi,

I agree with patrick for the same. Please give loops from each points eg; local MUX, SP each points. Please identify the segment in which the error occur.

Please check the local tail. a loop from modem towards the router. change the encapsulation of the link to HDLC and see if the link is coming up looped.Then ping to the own interface IP with a higher packet size and check for CRC increasing. Also check the router port as well. if these parts are clean , please push the Service provider to get a Bit Error meter and check the circuit.Also monitor clock received from the service provider as well. if it is varying and not a fixed one this can also create errors and slips in the link

I hope I have helped you a little.

Thanks and Regards,

Srinath.Muralidharan

Cable&Wireless

srinath.muralidharan@cw.com