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Old 05-16-2017, 03:40 PM   #1
LQ Newbie
Registered: Mar 2014
Distribution: Slackware
Posts: 16

Rep: Reputation: 2
tcpdump weird error about TLV length


I got a strange error from tcpdump which I cannot reproduce and I can't seem to find anything about it online.

The exact command I ran was this:
tcpdump -c 10 -vvnnSi bond0
Error I received:
Unknown TLV (0x00), length: 0
  Dissector error: print_unknown_data called with negative length
Even though I had the output limited to 10 packets only, the error was constantly being outputted to the terminal, forcing me to break it with CTRL+C.

I ran the command again to see if I can reproduce the error, but it ran fine and displayed 10 packets as instructed.

The machine is a SLES 11 SP1 x86_64 with tcpdump 3.9.8-1.21.

Does anyone have any clue what the above error means? Should I be concerned about this?
Old 05-17-2017, 02:42 AM   #2
Registered: Dec 2016
Location: Dublin
Distribution: Fedora
Posts: 70

Rep: Reputation: 4

You can dump the traffic to a file and post here, is only 10 packets . On the other hand, try to use wireshark also to see if is an issue with tcpdump. I know they use pcap for capture but your error looks like something on the decoders, probably due to the traffic on your device
1 members found this post helpful.
Old 05-17-2017, 12:55 PM   #3
LQ Newbie
Registered: Mar 2014
Distribution: Slackware
Posts: 16

Original Poster
Rep: Reputation: 2
Hey, camp0,

Yes, you are right. I can dump to a file. However, I can't reproduce that error. I have been running that command a few times and it ran just fine. If it happens again, I'll come back with an update. Maybe even a captured file.



linux, networking, packets, suse, tcpdump

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