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. And see here for current known issues.

New Member

Router's serial link having input errors.

Hi Wondering if anyone can help answer this problem, as my 1700 router's serial link is having constant input errors, every other minutes.

I have checked my modem which is working fine, changed a serial card. But the problem still persist. here is the "show int"


Serial0 is up, line protocol is up

Hardware is PowerQUICC Serial

Description: 2Mbps leased circuit to iASPire (Secondary)

Internet address is

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

reliability 255/255, txload 18/255, rxload 73/255

Encapsulation HDLC, loopback not set

Keepalive set (10 sec)

Last input 00:00:02, output 00:00:00, output hang never

Last clearing of "show interface" counters 3d06h

Queueing strategy: fifo

Output queue 0/40, 12617 drops; input queue 0/75, 0 drops

5 minute input rate 590000 bits/sec, 147 packets/sec

5 minute output rate 145000 bits/sec, 175 packets/sec

13727437 packets input, 3822921772 bytes, 0 no buffer

Received 32759 broadcasts, 0 runts, 0 giants, 0 throttles

20856 input errors, 525 CRC, 20206 frame, 0 overrun, 0 ignored, 125 abort

15015361 packets output, 3328324547 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

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



Wondering if anyone can advice?

Thanks and regards

Kum Fatt

New Member

Re: Router's serial link having input errors.

Hi ,

As per my point of vivew, I notice onething that CRC error, there my problem with line. so first give loop on modem towards router and check whether CRC error is incrasing if it incrase then problem should be on modem or V.35 cable. If it is ok then there will be problem at Line side,


Re: Router's serial link having input errors.

It may be the cable between the Telco interface and the router (csu/dsu).

If you are using Cat{anything} (UTP) between the NIU and the csu/dsu and it's longer than 3-4 meters (and especislly if it was a "home made" cable), then that's your most likely source.

UTP is not certified for use with T1/E1, though it it frequently used successfully for short distances. The specified cable for that kind of connection is "Premises Cable" ... which is individually shielded pair, inside a shielded sheath.

Prem cable should be good for ~655 feet.

If you want to see what it looks like, check out Anixter's website|catalog|search for "premises cable"

Good Luck


Re: Router's serial link having input errors.

Hi Kum,

Try replacing the cable between the CSU/DSU and your router. If you still have the errors, its more likely the telco issue. As posted by the first poster, Take telco people online and do the troubleshooting. You have to do the looping thing local at your end first and then check the remote loops.I have been on call manytimes for 3-4 hrs and have that problem solved completely.

HTH, Please rate if this helps.

-amit singh

Re: Router's serial link having input errors.



Can u explain me how loop test is done.



CreatePlease login to create content