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serial link problems over microwave

I have several remote sites connected via microwave links. There is an ongoing ‘battle’ within my group that provides the routers, and the telecomms group that provides the microwave link, as to the cause of intermittent link problems we seem to be having. In the case of today, the error log on routers on both sides of the link report %LINEPROTO-5-UPDOWN constantly.

A show int on the interface on one side of the link shows

Serial1/0 is up, line protocol is down

Hardware is M4T

Description: 384k Link to TZRD08 Kulsary CC

Internet address is (removed)

MTU 1500 bytes, BW 384 Kbit, DLY 20000 usec,

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

Encapsulation HDLC, crc 16, loopback not set

Keepalive set (10 sec)

Last input 00:13:06, output 00:00:07, output hang never

Last clearing of "show interface" counters 19:58:08

Queueing strategy: fifo

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

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

222083 packets input, 128854301 bytes, 0 no buffer

Received 0 broadcasts, 940 runts, 68 giants, 0 throttles

7622509 input errors, 4796745 CRC, 0 frame, 1271547 overrun, 365 ignored, 1554217 abort

206874 packets output, 91609712 bytes, 0 underruns

0 output errors, 0 collisions, 100 interface resets

0 output buffer failures, 0 output buffers swapped out

100 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up

The stats are from over a several week period, so I wouldn’t necessarily read too much into the high errors crcs etc, but there again it might be a symptom of the problem.

So is it a bad interface on a router, or is it the microwave link? How do I go about finding out?

The remote side is an hour’s drive away on bad roads so I’d prefer not to have to go on the road.




Re: serial link problems over microwave

Based on my own experience I would investigate the link.


- The ratio between good packets and error packets is very bad

- There are 100 interface resets. This is most likely saused by carrier loss

- At the time of the sh int, the link was down

My conclusion is that you have a bad link. The high error ratio is due to clocking errors. This type of problem could be wheater-related

For example: fog > bad link; clear skies > it works

You can also experience problems around sunrise and/or sunset.

New Member

Re: serial link problems over microwave

Thanks for your reply, I have seen fog cause problems. We've got blue skies at the minute, and this problem has been going on for about 24 hours now. It's -15C and has gone down to -24 recently though...

Do you know why there can be problems at sunsise and sunset?

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