I have two Cisco 1760 routers connect to each other by two T1 lines.
Recently they experience a strange problem : most of the time, only one line goes up, the other line goes down. And they "take turn" to go down.
And when one line go down, sometimes the CSU on the first router shows DCD/CTS down, other time the CSU on the second router shows those signals down.
In other word, one of the four CSUs on the two routers will take turn to show the DCD/CTS down.
I re-ran all the cables from the Smartjacks to the routers and replaced the CSUs on one router ( have not done for the other, but even on the router with replaced CSUs, sometimes it still shows the DCD/CTS down ).
I call the phone company and they confirmed that the loopback from smartjack to smartjack shows no problem, and from their site to each smartjack shows no problem.
Oops, I typed it wrong. I did add 'service-module T1 clock source internal' on one site, and the other does have the default value to be "source line". It does not solve the problem.
In fact, I have something strange on these T1 lines. The phone company told me they are point-to-point lines and I should provide the clock on one router. But when I turned the clock on, no line was up. When I turned the clock off all those two lines were working until recently when they take turn to go up and down.
R-1#sh int se 1/0 Serial1/0 is up, line protocol is up Hardware is PQUICC with Fractional T1 CSU/DSU Description: Second T1 to Sun Internet address is 192.168.245.5/30 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 00:00:00, output 00:00:00, output hang never Last clearing of "show interface" counters never Input queue: 1/75/0/0 (size/max/drops/flushes); Total output drops:
Well, first, I don't see the 'clock source internal' anywhere. I know you said you typed it, but I don't see it here. If this is in fact a P2P line, then one side must have it. I've seen places that work for a long time without it, then all of a sudden, there is a problem. Also, I notice a lot of CRC errors - this is the key. It could be caused by the timing, or maybe not. If you set the timing properly and still have the problem (clear the stats and then watch them), then next step would be to replace the cable from the T1 card to the smartjack. If you still have the problems, I would have the telco get involved again. It would keep you down for a while, but they could put a monitor on over night from site to site (something like a T-bird) that will give some good hard testing to the line. The loop backs they run from their office are only so good.
Could you, perhaps, have been getting a lot of rain lately? I've found that can often affect telco lines quite a bit.