Cisco router and a T1

[greenbird38]

We have a T1 connection that we use for voice over IP and connection to our server out of state. Frequently we loose connection to our T1 line and it quickly comes up after but happens all too often. Our ISP has checked the T1 connection from our Cisco router and found nothing wrong. The problem may have something to do with the router configuration or the wiring from the Router to our office. Can anyone give me some things to check on the router. It is a cisco 1700. I am familiar with some of the commands but wanted to get some advice. I can check the wiring, but can someone give me some advice on checking the router..
thanks,

 

[wybnormal]

Do a show interface on the serial port you use for the WAN connection. Look for high CRC error count, interface resets( interface loses keep-alive and/or LMI) or carrier transitions(link actually bounces down and back up)

You should clear the counters to start with a clean slate of numbers and watch it over a day or so. Consider using a SNMP tool like Solarwinds or MRTG to document errors.

Just because the Telco says it's fine, do not take them at their word.. I cant count how many times I've been told that and in the end, it's their problem. Documentation is your friend for this type of troubleshooting.

I'm sure others will add their favorite tricks to finding the problem to the list of suggestions here

MikeS
Find me at

http://www.packetattack.com

"The trouble with giving up civil rights is that you never get them back"

 

[BuckWeet]

I'd say this is a 100% telco problem, do you have any kind of external DSU that you could put a log on, say like an Adtran unit??


BuckWeet

 

[svermill]

What timing scheme have you implemented? Often times, these vanishing problems are clock slips.

 

[RadioX]

put a loopback plug on your serial interface to see if it is the interface itself

Check all your cabling from the serial interface to the smartjack

 

[greenbird38]

wybnormal? You mean connect to the router via hyperterminal and do these commands right. I can do that, thanks. As for Solar winds, I am interested in using this Bandwidth monitor. The server would have to be running SNMP? I am not sure I remember how to set up SNMP. And this cisco editor/viewer. This sounds cool too. I guess tommorow when I go in I will need to make sure that SNMP is setup before I go any further right?

And BuckWeet any kind of external DSU that you could put a log on, say like an Adtran unit?? I am afraid I dont know what this is.

And svermill? How would I check the timing scheme. I didnt set up this router.
Don't get me wrong I have handled servers and network tools, I am just a little inexperienced when it comes to cisco routers. I think I know enough to get me into trouble. I hope not any tips would be great.
Thanks guys..

 

[greenbird38]

RadioX I am going to check all the wiring tommorow. loopback plug on your serial interface? how do I go about doing that??
thanks,

 

[RadioX]

take a rj45 connector or what not and cross over pins 1,2,4, and 5 1 goes to 5 and 2 goes to 4. Plug it in, reset your counters, and you should see traffic on the interface. You should no receive and CRC errors and the interface should not jump up and down. should be clean traffic. You could also do this on the end of your cable that plugs into your smart jack. Start at the front (serial interface) and work your way out.

Hope this helps
Ron

 

[svermill]

You never said whether your CSU was internal or external. Does the RJ-48C plug directly into the router? Assuming it does, look at the interface setup with a 'sh run' on both ends of the circuit. There are a number of possibilities. You may find a 'service-module t1 clock source internal' statement on just one side and a 'service-module t1 clock source line' on the other. You may find the same command (line & line or internal & internal) on both ends. The correct setup depends on what telco is doing. If they are clocking the circuit via a Digital Access Cross-connect System (DACS), you need line & line. If they aren't, I recommend just one side be set internal and the other line.

The real reason I keyed in on clock is that in the case where it is misconfigured, the telco often sees the circuit as "error-free" while the user sees quite another thing. There are, of course, a hundred or so other possibilities. But config is always a good place to start -- especially where T1s are concerned.

 

[Tufbr8k]

You might look into utilization as well. That is a typical symptom of using too much bandwidth.

 

[wybnormal]

Green-

Just either telnet to the router to check the stats or use your trusty console cable and a laptop.

SNMP needs to be enabled on the router. Once that is done, you can use the tool of your choice to monitor it.

!
snmp-server community <string> RO
snmp-server community <string> RW
snmp-server chassis-id <string>
!

MikeS
Find me at

http://www.packetattack.com

&quot;The trouble with giving up civil rights is that you never get them back&quot;

 

[whatup]

Could be wrong but I believe the loopback plug is pin 1 to 4 and 2 to 5

 

[dddtran]

It is 100% a signalling problem..what is the router set on d4/ami or esf/b8zs..check for T1 alarms...like red, blue, or yellow alarms...Do test with the telco all the way thru..everyone must be using the same signalling...a loop test will not ID what the problem is b/c it is already in snyc..maybe use a T1 test set with the telco..do that until from point a to z..