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Problems with serial link

Answered Question
Jul 2nd, 2008
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Hi all.I have a problem in regard with a international serial link.I connected the serial interfaces with DTE cables on both ends but when I enter the show int serial command on both ends I get that the interface is up but the line protocol is down.On one side of the link I also see a lot of input errors and CRCs.

When telco establishes a loop I can see both interfaces go up(line protocol says it's looped as it should) but the second they remove the loop both ends go down.The link is achieved over an unmanagable network from point A to point B with classic TDM protocol.Any advice on what could be done to rectify the problem?Is this perhaps something a telco should resolve?

Correct Answer by Giuseppe Larosa about 9 years 1 month ago

Hello Igor,

site A does not receive the frames sent by the remote end



Last input 00:51:28, output 00:00:00, output hang never



while frames from A to B are flowing :


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



Site B is not able to receive correctly


72 packets input, 3540 bytes, 0 no buffer

Received 42 broadcasts, 0 runts, 0 giants, 0 throttles

7280383 input errors, 7280380 CRC, 2757891 frame, 8 overrun, 0 ignored, 2758028 abort


so there is a problem on local loop of site B


have the telco fix the circuit, this is a common problem




hope to help

Giuseppe

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Overall Rating: 5 (4 ratings)
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guruprasadr Wed, 07/02/2008 - 01:25
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HI, [Pls Rate if HELPS]


For Serial Interface @ DCE side ensure Clock Rate is configured and same not to be configured as DTE side.


Can you post your end - to - end Serial Configuration.


Pls Rate if HELPS


Best Regards,


Guru Prasad R



IgorHamzic Wed, 07/02/2008 - 01:34
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Thanks for the fast reply.I don't think the problem is with clock rate as I should be getting the clock rate from telco equipment on both sides of the link(they put the euipment to which I'm then connected with a serial cable on both sides)

The configs of serial interfaces are as folows(I'll add the show interface commands also):


Side A


interface Serial0/0

ip address 192.168.187.1 255.255.255.252

ip route-cache flow

no ip mroute-cache

no fair-queue

end


Serial0/0 is up, line protocol is down

Hardware is GT96K Serial

Internet address is 192.168.187.1/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

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

Encapsulation HDLC, loopback not set

Keepalive set (10 sec)

Last input 00:51:28, output 00:00:00, output hang never

Last clearing of "show interface" counters 18:03:15

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 0 bits/sec, 0 packets/sec

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

81 packets input, 11860 bytes, 0 no buffer

Received 43 broadcasts, 0 runts, 0 giants, 0 throttles

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

6619 packets output, 177528 bytes, 0 underruns

0 output errors, 0 collisions, 2163 interface resets

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

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


Side B:


interface Serial0/0/0

ip address 192.168.187.2 255.255.255.252

no fair-queue

end


Serial0/0/0 is up, line protocol is down

Hardware is GT96K Serial

Internet address is 192.168.187.2/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

reliability 128/255, txload 1/255, 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 00:53:11

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 0 bits/sec, 0 packets/sec

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

72 packets input, 3540 bytes, 0 no buffer

Received 42 broadcasts, 0 runts, 0 giants, 0 throttles

7280383 input errors, 7280380 CRC, 2757891 frame, 8 overrun, 0 ignored, 2758028 abort

566 packets output, 40620 bytes, 0 underruns

0 output errors, 0 collisions, 99 interface resets

0 unknown protocol drops

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

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


guruprasadr Wed, 07/02/2008 - 01:50
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HI, [Pls Rate if HELPS]


Possible Causes:


1.Local or remote router misconfigured


2.Keep-alives not being sent by remote router


3.Leased-line or other carrier service problems, such as noisy lines or faulty switch


4.Timing problem on cable, possibly caused by the CSU/DSU not being set correctly.


5.Failed local or remote CSU/DSU.


6.Router failure.


Please trouble shoot as above and check the results with your SP.


Hope I am Informative. Pls Rate if HELPS


>> Use the Rating System <<


Best Regards,


Guru Prasad R

paolo bevilacqua Wed, 07/02/2008 - 03:14
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Hi, you circuit is degraded and unusable:


Have telco fix it.


Please rate post if it helps.



Pravin Phadte Wed, 07/02/2008 - 04:03
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Hi,


You need to have an end to test with the telco.


This problems seems to be a telco problem and best option would be getting both the sites tested. Since you have said this is international circuit you need to involve your end telco and remote end to find out what the problem can be.


There can be also a possiblity that router chassai does not support the card. Get this verified too.


regards,


Pravin

IgorHamzic Wed, 07/02/2008 - 04:07
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A bit more info on the problem.I have asked the telco to estalish local loops and when they did I could see that both interfaces went up and no more errors were being registered on the problematic router.I could see the packets steadily coming in.

I also taught that perhaps the card is the problem but I've tested the link with another router with a serial card that I know that is 100% compatible with the same results.

I've now employed the telco to check things out because our network equipment isn't to blame as they claimed before.I'll keep you posted on the situation.

Correct Answer
Giuseppe Larosa Wed, 07/02/2008 - 05:48
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Hello Igor,

site A does not receive the frames sent by the remote end



Last input 00:51:28, output 00:00:00, output hang never



while frames from A to B are flowing :


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



Site B is not able to receive correctly


72 packets input, 3540 bytes, 0 no buffer

Received 42 broadcasts, 0 runts, 0 giants, 0 throttles

7280383 input errors, 7280380 CRC, 2757891 frame, 8 overrun, 0 ignored, 2758028 abort


so there is a problem on local loop of site B


have the telco fix the circuit, this is a common problem




hope to help

Giuseppe

IgorHamzic Wed, 07/02/2008 - 09:43
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Hello all.Finally the issue is resolved as telco finally corrected the problem.It was an uphill battle all the way and I want to thank you all for all your help.

paolo bevilacqua Wed, 07/02/2008 - 11:21
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Hi, do not worry, telcos always deny circuit problems. They are programmed like that.


Thanks for the appreciation and good luck!

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