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Cisco 1720 - Many Input Errors, CRC and the like

Posted on 2004-09-02
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Last Modified: 2010-05-18
Dear Experts:

A little about my setup:

I have a Cisco 1720 Connected to a Fractional T1 through a phone compnay owned CSU/DSU.  We are using 7 timeslots, or 448k.  This is our border router and is used strictly at this point as our Internet Connection and that is all.

Auditing the interfaces, I noticed the listed below show interface serial 0 command with many input errors.


MTU 1500 bytes, BW 448 Kbit, DLY 20000 usec,
     reliability 255/255, txload 4/255, rxload 19/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:04, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops)
     Conversations  0/24/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
  5 minute input rate 34000 bits/sec, 6 packets/sec
  5 minute output rate 8000 bits/sec, 6 packets/sec
     3020709 packets input, 2582061765 bytes, 0 no buffer
     Received 124253 broadcasts, 0 runts, 5 giants, 0 throttles
     8570 input errors, 1664 CRC, 1345 frame, 0 overrun, 0 ignored, 5558 abort
     2485337 packets output, 300385519 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
     9 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

Now, considering the error rate % is .003% -- not too bad, and I'm not particularly noticing any performance issues.  The last time I cleared this counter was about a 10 days ago.

Things I have Checked:

* I have taken the router to the Smart Jack in the Phone Room and plugged directly in, same results as far as error incrementing.  This elimated the cabling between CSU/DSU and Router.
* I have called our ISP who called CTSI (our phone company) and they apparently came on site when I wasn't hear and tested their equipment, they had no troubles. (this doesn't surprise me)
* Phone company says there must be something wrong with your Router

Is there anything else I should focus my eyes on with this type of problem?

I was reading another post and they used the command show controllers serial 0, and that shows me another little bit of info (i guess it reads the Serial Card directly)?  Here the end of that information.

buffer size 1524

PowerQUICC SCC specific errors:
5558 input aborts on receiving flag sequence
0 throttles, 0 enables
0 overruns
0 transmitter underruns
0 transmitter CTS losts

I hate dealing with the phone company, they are always perfect.

Deeky
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Question by:deeky
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by:lrmoore
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>   8570 input errors, 1664 CRC, 1345 frame, 0 overrun, 0 ignored, 5558 abort

Definately points to telco problems, especially since you have ruled out the wiring by going directly to the smart jack.

Did they reboot the CSU/DSU?

Clear the counters again. I'm dealing with same issue with our provider. 500 - 1000 errors per day. Statistically, that's not much compared to the data packets, but it is still too many for me and I won't let the phone company off the hook (close the ticket) until I can run 48 hours with zero errors...
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by:deeky
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Any suggestions about how to approach them, I like to sound intelligent when I contact them.  The errors seem to be most prevalent when traffic levels are high.  I mimick this by downloading a large file.

I reset 20 minutes ago and I have 22 input errors, 10 CRC and 12 Frame.

It just bugs me.

I'll contact them again and see what happens.  Can I loopback on my router interface or somehow bench test my router to make sure that it is not a hardware failure?  Would I be able to swap the Serial card into the other WIC slot?

One other thing, I never saw the cooling fan run in my 1720, is it controlled by a thermistor or is it supposed to run continuously.  My server room is A/C and about 68-70 all year, so maybe I never had it hot enuf.

Deeky
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by:lrmoore
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Be sure to tell them that you are getting CRC and frame errors, at an unacceptible rate, and that you will not close the ticket until you see it run clean. Ask them if they rebooted the CSU since they own it...

I seriously doubt that it could be heat related. I think the fan is controlled, but, hey, it's worth looking into..
I'll see what I can find out about it.
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by:deeky
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One more thing, I notice that my Ethernet side of router has CRC problems.  It has a cable running between the NIC of the Linux Firewall and the Fast port on the router, can't be longer than a few feet.  I wonder what is up with that?

Deeky
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by:deeky
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Well, I'm creating a self-administered forum.  I have fixed the ethernet CRC problem all by myself with a new cable.  Sometime I just need to put my problems in writing.

I sent another trouble ticket to CTSI.  I did unplug and restart the CSU/DSU myself, I don't know if that if sufficient to reboot it or if their is a hardware reboot.

Deeky
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by:stealth188
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You want to make sure that your clocking is setup correctly.  Since the T1 is for internet access you are getting the service from some provider.  Check with the ISP, not the phone company, and ask how they have the clocking setup.  Most ISPs will be the "master" and the customer the slave.  If that is the case with your ISP make sure you are deriving your clocking from the line.  Something like "clock source line".  Good luck
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by:deeky
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I have been contacted by our phone company.  They have monitored our circuit for three days and did not see any problems.  Their position on the matter is that their outgoing interface is not seeing any output errors, therefore, there is not a problem with the phone companies loop or hardware.

They keep suggesting possibly my WIC card is failing.  I doubt that, but don't have much experience with them.  I wonder the likelihood that the CSU/DSU in our phone room, having probably been misconfigured or having some type of hardware problem.

Deeky
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lrmoore earned 250 total points
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If you have an external CSU/DSU, it could be failing, or it could be a clocking configuration, as stealth188 points out.
I'm still fuzzy about your configuration. You need to eliminate all possible parts that you own:

          router----serial interface----serial cable (v.35?) ---- CSU/DSU----cable (cat5? 4wire?) --- smartjack
   possible failure points ^^                ^^                           ^^             ^^                               ^^          

Serial interface itself is unlikely, but not unheard of. Look at output from "show controllers" and look at "specific errors". What you've shown above is 0 errors. Any failures would surely show up there.

Serial cable has two ends - 60-pin serial (or tiny smart serial) and v.35 (or rs532) - check for loose, bent pins
CSU/DSU configuration - line build-out settings, clocking, etc (if telco owns it, they should be able to make sure it is OK and rule it out)
Wiring between CSU/DSU network port and the smartjack. Every possible connection, cable end or punch-down is a source of potential loose connection.
Smartjack itself. Telco should be able to rule this out because they are the only ones that can access it.

Lastely, it could just be some minor static in the lines due to weather in the area, or other phenomenon that will just clear up on its own..

If you have ruled out your pieces, and are still experiencing CRC and frame errors, then call them back and tell them you will not release the ticket until you run clean with no errors for a minmum of 48 hours.      
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Author Comment

by:deeky
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Here is what it looks like

router ----- wic T1 DSU Interface Card (RJ45 JACK to Cat 5e cable) [ I call it the SERIAL Interace ] ---- 250' run to phone room ---- smartjack ---- CSU/DSU ---- Phone Wire to Outside

Would that be a fact though that is they are not seeing output errors on our circuit that input errors that we are receiving are caused by problems in our internal phone system?

BTW, while you mentioned serial cables, which I have seen before on some old routers I have at home, they have 60 pins.  Why so many, serial connection would generally need 4 at most?  + - send + - receive.  Obviously, that is not how these cables and interfaces work.  What would 56 other conductors do in those "serial" cables do ?

A little off topic, but you sparked another curiousity.

Deeky
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by:lrmoore
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OK. Is your router serial interface set for defaults? Can you post up your serial 0/0 config?


I guess so many pins so that they can provide a single interface to a multitude of different connections, sync or async, v.35, rs232, rs532, rs442, whatever. I'm sure each type requires a tad difference, but the pin density makes it possible for almost any combination.

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by:deeky
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interface Serial0
 ip address 199.xxx.xxx.xxx 255.255.255.0
 ip nat outside
 service-module t1 timeslots 1-7

This is an excerpt from Running Config for just serial 0.  SHort and sweet.

Deeky
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by:lrmoore
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it looks a little odd that you are using 7 timeslots. Typically it is an even number. I've never seen a 448k link...
What is your port speed supposed to be?
256k = 4 channels
384k = 6 channels
512k = 8 channels
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by:deeky
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Well, we started out with 2 channels, or 128 kbps.  About 9 months ago we upped to 512 kbps, but as it turns out, we had too many voice channels used.  So, we decided to utilize all available empty channels, going to 7 with 448kbps.  That is why it is an odd number.  Could this possibly be a problem?  I remember the phone company  tech had an issue with the A side and B side of the CSU/DSU being programmed because we had to use both sides for some reason, and they had to be channels adjacent to each other.

Anyhow, like I said, a simple configuration for the interface.
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by:deeky
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What do you think of the logic behind their arugument that their router is not seeing output errors on our circuit, yet we see input errors?

Deeky
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by:lrmoore
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It could be a channel mismatch between their DSU and your DSU....

From their perspective
YOU Tx -----output----> THEM  <== they are not seeing output errors from you
YOU Rx <----- input ---- THEM  <== you ARE seeing input errors from them
It's a duplex line. You're not sending errors, your REceiving errors. FROM THEM..
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by:deeky
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I have had no luck with communication with the phone company and would like to close the question.  I'm assuming the phone company is at fault, but I'm too dumb to prove it.  Until error level reach above 1%, which they are much below, I will have to deal with it.

Hopefully by then we will switch back to Verizon for the good service we were used to.

Moderaters and participants, I'm not familiar with the procedure to close a question like this.  I would certainly like to award points to lrmoore for his help and clear explanation.  However, since the issue did not get resolved, would that be appropriate?

Deeky
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by:lrmoore
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The question is yours, so whatever you think is fair. If any of the comments helped you at all, you should accept.

Sorry we could not be more help...

Thanks!
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