Cisco WAN config troubles.

[necom]

I have a point to point setup and 2 Cisco 1720's (one at each end), for some reason when I connect the routers to the smartjack, the light go green and look good, but it keeps changing from LINK up to down and then up again about every 30 seconds (flapping). Everything is at default, this looks like a layer 1 problem so I havent really done much in the way of configuration. Telco says their stuff looks good. One more side note, I cant ping the serial interface either (from CLI), but if I remove the cable to the smartjack and replace it with a loopback plug it comes up and I can ping it fine. Any ideas?

 

[watchguardmonkey]

sounds as if you have either a duff cable or your using the wrong type, you might be using a Xover when you need to use a straight through or vice versa.

 

[jneiberger]

How do you have your clocking configured? One side should be set to take clock from the line and the other should be set for internal clocking.

 

[necom]

I'm using a straight through cable (although it is pretty long, maybe 250-300 feet), on the clock question, I tried it with one side using line and the other using internal. No luck either way.

 

[jneiberger]

Do you have internal or external CSU/DSUs? Are they configured for the proper number of channels? Is this a full T1 or fractional?

 

[necom]

Internal csu, configured for full. Would CSU/DSU settings in the router cause it to flap like this? The only settings I've done for the serial interface is

IP address/mask
so shut
service-module t1 timeslots 1-24
b8zs, esf (confirmed through telco)
bandwidth 1544
clock source internal (line on other side)

Thats pretty much it. The flapping seems like a layer 1 problem, wouldnt you think? By the way, if I use a crossover cable and go from S0 on one router to S0 on the other (taking the t1 out of the equation), everything works fine.

 

[jneiberger]

You have a T1 from your service provider, yet they're close enough to connect back-to-back? ;-)

This sounds like a telco problem to me. Put a loopback plug on your side of the Smartjack and then see if they can see the loop. Many times they'll loop to the front side of their equipment and it will test clean. However, if the problem is inside the smartjack then you need to be able to test through it to verify.

 

[necom]

They've already tested it, they say their stuff is good.

 

[jneiberger]

Did they test it while you had a loopback plug in their smartjack? That's the test I was recommending.

 

[necom]

Yes.

 

[JOAMON]

Think you need to look at the 300' plus cable. If you have a cable tester you should test it. If no cable tester could bring router close to the Telco equipment and connect with a short straight through cable. If it works then it must be the other patch. Also in the 300' run to the router is their possibly any source that may be causing EMI interference?

 

[necom]

I'm not sure if there is any other interference. I'll be out there tomorrow with 1 new router and the two originals to test. I'll connect directly to the smartjack with a short cable and see what happens.

 

[directlyconnected]

Uh, that cable seems a bit too long. 100 meters is a little over 300 feet...

 

[jeter]

Heres what I would so. Move you routers into the location of the NIU (Network Interface Unit) in plug right into the smart jack. After you have done this and you still have a problem put a loop on the smart jack and veriry the other end. Also loop your CSU/DSU again to re-verify a good connection. If possible pull out and reconnect the circuit boards in the NIU. These lock up from time to time. Has far as the distance of 300 ft you should be okay because most carriers pad the circuit to be extended I heard up to 1000ft but that a streach. Last question how is your cable from the dmarc to your equipment wired? Remember T1's use pins 1,2,4, and 5

“Reserve your right to think, for even to think wrongly is better than not to think at all”

CCNA,CCNP,CIPT, Network+
Tek-TIP Member 19,650

 

[necom]

Hi jeter, I'm using a straight through cable (standard patchcord pinout). Are you saying that if I put a loopback plug in the NIU on one end, the other end should show loop? I ask because I tried that to see if it would bring up the router on the other side in a loopback state, it did not.

 

[necom]

Update: Finally, today its working. It was the telcos problem (SBC).