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New Member

Malformed Packets and Bad Checksums

..I have a customer who uses MPLS to connect to all remote locations. The MPLS carrier has recently merged with another carrier, and they are in the middle of making changes to their MPLS network(s). As a result, some (but not all) of my customer's sites that have gone through these changes are having problems with one particular application only. Wireshark packet captures at the remote location and at the affected application server shows the following, among other things:

- Bad IP Checksum

- Malformed TDS Packets

- Malformed SSL Packets

- Malformed GSM over IP Packets

- Malformed ASAP Packets

- TCP Sequence out of order

- ACKed lost TCP segment

- Previous TCP segment lost

- Fast TCP retransmission suspected

This is only a subset of the problems that Wireshark shows. The strange thing is that only a subset of the remote sites are affected, and it really is only one particular application of a large suite of applications. All other applications work acceptably. In addition, other sites that have been converted work just fine as well. There are about 15 of 80 sites having thus problem. The MPLS provider of have reviewed their equipment and configurations. Unfortunately, after the changes were made, we have no visibility into the MPLS network (it just shows one hop), so I have no way of helping them to troubleshoot.

We have the ability to test the application using a site that is connected via Fiber, and the application works just fine. Of course, we have moved PCs, etc from site to site. The problem seems to stay with the site, rather than the computers.

Any advice or ideas on what I can do to test would be appreciated.

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Cisco Employee

Malformed Packets and Bad Checksums


there is lot of interesting troubleshooting to be done  Yours is the type of case I loved when I was in the TAC as I enjoyed using creative ways to investigate and tackle similar problems.

there might be so many approaches for this that I have difficulties to list them all.

I am afraid that a CSC post is not the right place for that as this can be time comsuming and lot of effort is needed.

I suggest you to open a TAC case where you can find some engineer with the right mind set for this CSI type of troubleshooting.



New Member

Re: Malformed Packets and Bad Checksums

OK, thanks for being honest with me about it. Take care.


Jason Dell

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