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New Member

Serial line---gateway router

Hi All,

On my gateway router,

1)I am getting crc error and large number of packet drops in serial line(V.35, connecting to VSAT modem). How can I troublshoot these?

Serial0/0 is up, line protocol is up

Hardware is PowerQUICC Serial

Internet address is

MTU 1500 bytes, BW 4096 Kbit, DLY 20000 usec,

reliability 255/255, txload 68/255, rxload 74/255

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 00:49:32

Input queue: 0/75/54/0 (size/max/drops/flushes); Total output drops: 8780

Queueing strategy: fifo

Output queue :0/40 (size/max)

5 minute input rate 1197000 bits/sec, 1406 packets/sec

5 minute output rate 1093000 bits/sec, 1557 packets/sec

4384424 packets input, 466717463 bytes, 0 no buffer

Received 297 broadcasts, 0 runts, 0 giants, 0 throttles

1 input errors, 0 CRC, 1 frame, 0 overrun, 0 ignored, 0 abort

4067601 packets output, 364542153 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

Above is after clearing the counter of serial interface.

2)I am also worried about the 'txload' and 'rxload', is it ok?

3)What should be the BW on this s 0/0, as my upload is 2.5Mb/s and download is 1.5Mb/s for VSAT, I configured it( s 0/0) for 4Mb.

Thanks in advance,



Re: Serial line---gateway router

You should check th transmission facilities serving this interface (starting from router interface to the remote end). 1. RX/TX loads are OK. 2. Some Dynamic routing protocols calculate their interface metric according to the output BW, so your BW calue for this interface should be equal to your physical output data rate.

New Member

Re: Serial line---gateway router


I actually don't understand "transmission facilities serving"? What is it?

Otherthen, it is ok.

Thanks for your reply.


Re: Serial line---gateway router

Sorry, I meant the transmission equipment and lines providing transmission service between your interface and the interface on the other side (end-to-end). CRC and other physical errors may be caused by noisy transmission lines, loose connections or faulty transmission equipment. For troubleshooting of serial lines you can consult the document:

This document provides a detailed explanation of errors, causes and troubleshooting methods.

Re: Serial line---gateway router

Another point is about drops, I forgot to write about them. Your interface is experiencing some input and a large number of output drops (if these ar not old values). Clear the interface counters using clear counters command and monitor the interface using sh interface command. If there's still an increase in drop counters probably the in / out bandwidth provided by this serial line isn't enough for the traffic feeding the router. For example if an ethernet interface is feeding the router and it's traffic is exceeding the value the serial can handle, drops occur.