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Cisco PTP T1 Config

We have a Point to Point T1 between two locations (about 150 miles apart).

I had installed a Cisco 1941 router at each location and it's been working fine for about 3-4 weeks, then this past week, it started dropping a lot. I have a ticket open with ATT, but they are doing their normal thing and starting to come back to me saying it's a issue with our equipment, but I really don't think so as it' worked perfectly for about 3 weeks.

My cisco config on the serial interface is very simple:

interface Serial0/1/0
 ip address

That's one end, then the other is

Is there anything wrong with that?  Like I said this worked for several weeks then just in the past week we started having issues.
Network OperationsRoutersNetworking

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8/22/2022 - Mon

That is the basic way to setup an interface.

You should be able to ping between the two sides from the routers.

You may want to do a:

sh interface serial 0/1/0

See if you see any CRC errors or other stuff that might indicate an issue with the line.

Yeah I can ping so I know that parts good..just wanted to make sure.

I do have several thousand interface errors and a few million crc.

I'm making the provider test their lines, just wanted to make sure I wasn't missing something.

No, if sounds like line trouble...  

I'd send them a screen shot...  Maybe clear the counter and see how fast it climbs afterward.  

If it goes down, login to the router and check the interface status.  I'd imagine you are getting packet loss too if you ping hard and long enough.
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James Murphy

I've copied / pasted my sh int s01/0 results and sent  that to them.

if I clear counters I'm at 1.5 million CRC errors in 12 hours.

Thanks for the help.
Steve Jennings

That's crazy . . .CRC errors that high are almost always due to a noisy line . . .but I would still power cycle both routers just to make sure.

Good luck,

Well the ISP came back and said it's our equipment.

They hooked up their TBIRD and said it ran clean, even though I still got all those CRC errors.

I'm going to hook both routers together with a T1 crossover to show them that the equipment is fine.
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I've never seen errors occur beyond noise/line issues.  You may want to do what Steve suggests and make sure the T1 card's are snug in the routers.
Steve Jennings

That will be a neat trick if they are 150 miles apart.

Sorry, couldn't resist.

Is your connection from a smart jack or a patch panel? Perhaps someone wasn't careful while working in your wiring closet.

If they have looked at the line and they say it's clean (between their CSUs) and yet you are seeing that many CRC errors, you may very well have a hardware problem. If it's a "soft" problem, power cycling may help. There may be a clocking or framing issue in one of your cards that was caused by their testing.

Good luck,

I'm actually going to take a spare router down to one location tomorrow and test it, then if that tests clean I'll take it to the other location then next day.

What about clock source?

Do I need to specify a clock source on both controllers?
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You were right.

I changed one router to have it's clock source as internal, and that fixed it all.