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release 3.6.8 missing SEQ/ACK analysis

asked 2022-09-12 19:50:19 +0000

JohnH gravatar image

I must be missing something, since I upgraded from 3.4.6 to 3.6.8 I no longer see the SEQ/ACK analysis section under TCP. I checked by loading the same capture in both versions. I have also unchecked - Do not call subdissectors for error packets - in both versions. In 3.4.6 I can use the filter TCP.Analysis.duplicate_ack and I find 34127 dup acks. I have looked at the actual dup packets to validate these are real dups and they are. When I load the same capture in 3.6.8 the same filter finds 0 packets and the SEQ/ACK analysis section is missing. Help!

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Is it possible that Analyze Sequence Numbers is not enabled/checked in your preferences for TCP?

Chuckc gravatar imageChuckc ( 2022-09-12 21:45:56 +0000 )edit

Analyze Sequence Numbers is enabled, here are the enabled TCP preferences;

  • Show TCP Summary in protocol tree,
  • Allow sub dissector to reassemble TCP streams
  • Analyze TCP sequence numbers
  • Track number of bytes in flight
  • Calculate conversation timestamps
  • Try heuristic sub-directors first
  • TCP Experimental Options with a Magic Number

All the rest are disabled

JohnH gravatar imageJohnH ( 2022-09-13 11:52:10 +0000 )edit

There is a sample capture on Wiki page for TCP.
Open it in 3.6.8 and see if working. If not then a config issue. If it does work then something in your capture and would be easier to move forward if you can share the capture file.

A display filter of tcp.analysis will show the packets with a [SEQ/ACK analysis] section.

Chuckc gravatar imageChuckc ( 2022-09-13 15:10:34 +0000 )edit

I have loaded the sample capture and it appears to work. How do I share the capture file I am working with?

JohnH gravatar imageJohnH ( 2022-09-13 15:22:45 +0000 )edit

Put it on a public file share (Google, Onedrive, Dropbox, ...) then update the question with a link to it.

Chuckc gravatar imageChuckc ( 2022-09-13 15:30:23 +0000 )edit

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answered 2022-09-13 15:59:50 +0000

Chuckc gravatar image
Snapshot length: 64
[Packet size limited during capture: TCP truncated]

This is an open issue: 18138: Incomplete captured TCP packets not registered as conversations.

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Thanks for looking into this, at least I'm not crazy. Any estimate on when or which release it might be fixed in?

JohnH gravatar imageJohnH ( 2022-09-13 16:01:26 +0000 )edit

Can you increase the snap length when capturing? See notes here:
You could also add a comment to the open issue showing your interest in moving forward with the Draft commit.

Chuckc gravatar imageChuckc ( 2022-09-13 16:06:58 +0000 )edit

What snap length would you recommend. Most of my customers want to use a minimum snap length to minimize exposure to their customer data. I will use this in the future, in this case I was going over some old captures to put together problem determination training when I discovered the issue. I should have red the notes first, it looks like 94 bytes would work reliably.

JohnH gravatar imageJohnH ( 2022-09-13 16:16:49 +0000 )edit

Definitely test before you have to rely on that for a solution.

Chuckc gravatar imageChuckc ( 2022-09-13 17:02:19 +0000 )edit

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Asked: 2022-09-12 19:50:19 +0000

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Last updated: Sep 13 '22

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