[c-nsp] Need help troubleshooting CRC errors

[Antonio Soares]

This document might help you:

Understanding Maximum Transmission Unit (MTU) on ATM Interfaces

http://www.cisco.com/en/US/tech/tk39/tk371/technologies_tech_note09186a00800c8279.shtml 

This is what it says about Length Violations:

"A router increments the AAL5 length violation counter when the calculated size of a reassembled packet fails to match the received
value of the AAL5 length field regardless of the MTU. To understand how these violations can occur, you need to understand how a
receiving ATM interface recognizes the last cell of a frame."

What ATM NM do you have in the 3640 ? Did you change the default MTU from 4470 to 1500 ?



Regards,

Antonio Soares, CCIE #18473 (R&S)
amsoares at netcabo.pt

-----Original Message-----
From: Steven Pfister [mailto:SPfister at dps.k12.oh.us] 
Sent: sexta-feira, 18 de Setembro de 2009 19:09
To: Antonio Soares; cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] Need help troubleshooting CRC errors

Thanks for the link... I have a little more detail about the problem now:

'show atm pvc x/y' shows:

CrcErrors: 69402, SarTimeOuts: 2, OverSizedSDUs: 0, LengthViolation: 69294, CPIErrors: 0

Also, the router side shows, on 'show int':

  MTU 1500 bytes, sub MTU 1500, BW 155000 Kbit, DLY 80 usec,

router side, on 'show atm int atm':

Max. Datagram Size: 1558

8510 switch side, on 'show int':

  MTU 4470 bytes, sub MTU 4470, BW 155520 Kbit, DLY 0 usec,

Would this be a problem?

Steve Pfister
Technical Coordinator,
The Office of Information Technology
Dayton Public Schools
115 S. Ludlow St. 
Dayton, OH 45402
 
Office (937) 542-3149
Cell (937) 673-6779
Direct Connect: 137*131747*8
Email spfister at dps.k12.oh.us


>>> "Antonio Soares" <amsoares at netcabo.pt> 9/17/2009 11:45 AM >>>
Try this document:

CRC Troubleshooting Guide for ATM Interfaces

http://www.cisco.com/en/US/tech/tk39/tk48/technologies_tech_note09186a00800c93ef.shtml 


Regards,

Antonio Soares, CCIE #18473 (R&S)
amsoares at netcabo.pt 

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Steven Pfister
Sent: quinta-feira, 17 de Setembro de 2009 15:39
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Need help troubleshooting CRC errors

Some of our older remote sites are connected via ATM. Two or three T1s come into an Cisco 8510, and from there a 155mbps OC3
connection over fiber to a 3640 router. Lately, I've been noticing that pretty much every one of them is showing what I think is a
rather high receive error count on the 3640 end of the OC3 connection, and it all seems to be CRC errors. Not much of any errors are
showing up on the 8510 end of the OC3 connection. For example, one site yesterday late afternoon showed 63, 763 receive errors for
the day. Several others were in the 20Ks. I'm not really certain what the cause might be, or where to start. Can anyone help?

Thanks!


Steve Pfister
Technical Coordinator,
The Office of Information Technology
Dayton Public Schools
115 S. Ludlow St. 
Dayton, OH 45402
 
Office (937) 542-3149
Cell (937) 673-6779
Direct Connect: 137*131747*8
Email spfister at dps.k12.oh.us 


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