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Getting CRC and fram errors on serial ppp point 2 point T1 connection

Posted on 2003-03-28
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Last Modified: 2012-08-13
Hello,

I have a client that is complaining about corrupted files whenever they send the files over their point 2 point T1 connection to the other office.  I looked at the routers on both sides of the T1 (Cisco 2621XM routers) and noticed that in router A there are 17 CRC errors and 7 Frame errors since I reset the couters 6 hours ago.  I believe this is why the  clients files are corrupted.  Can anyone tell me how I can further troubleshoot this.  (Been a while since my cisco course) what can cause CRC and Frame errors on a ppp encapsulated point to point T1 connection between two Cisco routers.

thanks
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Question by:Lionel_
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9 Comments
 
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lrmoore earned 750 total points
ID: 8228723
CRC and frame errors are caused by several things, usually having to do with either the CSU/DSU, the cable, or the T1 line itself.
Are they using T1 DSU module in the router, or external DSU?
Either case, check the clock source on both ends. If it is PPP leased line, is the telco expecting one end to provide the clocking?
Is there a T1 demark extension? Who ran the extension?
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Author Comment

by:Lionel_
ID: 8234295
Neither of the routers provide clocking. I guess I should configure one to provide the clocking. I though of this before but since the line was otherwise working and this only happens with large video files going over the T1, I didn't do it.

Each of the routers have a DSU card in a serial slot.
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by:lrmoore
ID: 8234402
you would need to check with the telco provider to see if they are providing the T1 clocking. If they are, then both of your ends should be set to clock source line.
Have you changed the MTU size at either end?

Do you have an extended demarc? Very often this is the cause of the line errors.
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Author Comment

by:Lionel_
ID: 8234542
No extended dmarc, MTU has not been changed and is set at 1500, don't know if telco is providing clocking, however, come to think of it, they must right, if most packets are transversing the line.

Thanks!
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LVL 79

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by:lrmoore
ID: 8234619
What do your counters look like now? A very few should not cause any problems. 17 in 6 hours is not too bad. If it continually increases and gets into the hundreds, then I'd call the telco. Static on the circuits can also cause it. Any dropped packets?
You might need to have the telco dispatch someone to come out and run a bert test on the line.

From Cisco's documentation:
"if you get cyclic redundancy check (CRC) errors, a bit error rate tester (BERT) with an appropriate analyzer from the telco is needed."
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LVL 79

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by:lrmoore
ID: 8234630
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LVL 79

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by:lrmoore
ID: 8442663
G'day, Lionel_
It has been 34 days since you posted this question.
Do you still need help? Have you received enough information?
Can you close out this question?
Ways to close questions: http://www.apollois.com/EE/Help/Closing_Questions.htm
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LVL 79

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by:lrmoore
ID: 8725675
Lionel_,
No comment has been added lately (44 days), so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area for this question:

RECOMMENDATION: Award points to lrmoore

Please leave any comments here within 7 days.

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!

Thanks,

lrmoore
EE Cleanup Volunteer
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please post comments here where a Moderator will see it.
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Author Comment

by:Lionel_
ID: 8727075
I am sorry for not following up with this thread.  The problem wound up being related to the auto duplexing on both sides of the router.  Once I hard set that config to full duplex on both sides the crc errors ceased.  The corruption however was discovered to be related to a Mac OS issue.  OS9.2 has a limitation transfering files that are larger than 2 gb. That is where the corruption took place.  I would award the points to lrmoore for his efforts.

Again I appologize for not being a bit more diligent with this.
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