ATM/IMA Link dropping packets

Unanswered Question
Nov 13th, 2008

Hi all,

I have a Problem with a ATM service Dropping large Packets, If I ping with a packet size of 500 it goes fine. And if I use 1400 it drops 60% of the packets.

Can anyone see any obvious Problem in the show command below?

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ROUTER-WAN#show ima interface atm 0/ima0 detailed

Interface ATM0/IMA0 is up

Group index is 28

Ne state is operational, failure status is noFailure

IMA Group Current Configuration:

Tx/Rx minimum required links 1/1

Maximum allowed diff delay is 25ms, Tx frame length 128

Ne Tx clock mode CTC

Test pattern procedure is disabled

Detailed group Information:

Ne IMA version in operation IMA Version 1.0

Fe IMA version in operation IMA Version 1.0

Tx/Rx Ima_id 0x11/0x0

Ne state operational Fe state operational

Ne symmetry symmetricOperation Fe symmetry symmetricOperation

Number of Tx/Rx configured links 2/2

Number of Tx/Rx active links 2/2

Ne clock mode ctc, Tx frame length 128

Fe clock mode ctc, Rx frame length 128

Tx/Rx timing reference link 0/1

Maximum observed DCB depth 2 cells, Maximum DCB depth 1 cells

Maximum observed diff delay 0ms, Maximum diff delay 0ms

Least delayed link 0, Most delayed link 0

GTSM last changed 09:39:02 WST Thu Nov 13 2008

IMA Group Total Counters (time elapsed 88411 seconds):

21464978 Tx cells, 40432199 Rx cells

1 Ne Failures, 1 Fe Failures, 32 Unavail Secs

Detailed IMA link Information:

Interface ATM0/0/1 is up

ifIndex 18, Group Index 28, link exists and is operational

Tx/Rx Lid 0/1

Ne Tx/Rx state active/active

Fe Tx/Rx state active/active

Ne Rx failure status is noFailure

Fe Rx failure status is noFailure

Tx/Rx test pattern 0x0/0xFF

IMA Link Counters

0 Ima Violations, 0 Oif Anomalies

15 Ne Severely Err Secs, 10 Fe Severely Err Secs

1 Ne Unavail Secs, 1 Fe Unavail Secs

14 Ne Tx Unusable Secs, 14 Ne Rx Unusable Secs

13 Fe Tx Unusable Secs, 13 Fe Rx Unusable Secs

0 Ne Tx Failures, 1 Ne Rx Failures

1 Fe Tx Failures, 2 Fe Rx Failures

195455 Tx stuff events, 195405 Rx stuff events

Interface ATM0/1/0 is up

ifIndex 23, Group Index 28, link exists and is operational

Tx/Rx Lid 1/0

Ne Tx/Rx state active/active

Fe Tx/Rx state active/active

Ne Rx failure status is noFailure

Fe Rx failure status is noFailure

Tx/Rx test pattern 0x0/0xFF

IMA Link Counters

0 Ima Violations, 0 Oif Anomalies

116 Ne Severely Err Secs, 7 Fe Severely Err Secs

1 Ne Unavail Secs, 0 Fe Unavail Secs

115 Ne Tx Unusable Secs, 115 Ne Rx Unusable Secs

14 Fe Tx Unusable Secs, 14 Fe Rx Unusable Secs

0 Ne Tx Failures, 1 Ne Rx Failures

1 Fe Tx Failures, 2 Fe Rx Failures

195495 Tx stuff events, 195221 Rx stuff events

I have this problem too.
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Giuseppe Larosa Mon, 11/17/2008 - 11:13

Hello Mohammed,

I don't see anything wrong in your show command.

the packets are sent in 128 bytes fragments so also the 500 bytes are actually sent in multiple fragments.

What changes is the number of fragments that have to wait on the SAR buffers to be rejoined and then the ip packet is extracted from the AAL5 PDU.

If there was any MTU issue the loss rate should be 100% not 60%.

Calculations should be done in ATM cells to see if there is a different ATM bit rate (as we can expect) and compared to the CIR provided by the service provider (if this isn't a back to back configuration)

Another note is that an ATM IMA vers.1.1 exists and your router is using version 1.0

Hope to help

Giuseppe

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