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How to display VLAN and info from unkown protocol

asked 2023-03-10 10:45:56 +0000

nignasi gravatar image

updated 2023-03-10 22:47:11 +0000

Guy Harris gravatar image

We use a program which builds ethernet frames which contain 802.1Q info followed by a text to fill the frame. We don't include higher level protocols into the frames. The contents is some informative text or just dummy content. We use the undefined 0x8000 identifier into type field after VLAN bytes.

So a frame shows something like 0x8100 0xa001 0x8000 ... after MAC source address.

Wireshark reads 0x8100 and shows 0xa001 VLAN parameters into Info column (PRI: 5 DEI: 0 ID: 1), afterthat reads 0x8000 which is shown into Protocol column (and with "Type: Unkown (0x8000)" message in paquet details window) but the following payload is not shown in paquet list window because Info column is occupied by the VLAN info.

I've found a possible Vlan ID column, but not how to show all this information into a new column while kipping the Info one for the text/dummy contents of our frames. How can we do it?

Thank you

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answered 2023-03-10 13:47:25 +0000

Jaap gravatar image

The info column is filled by the protocol dissector that is handed (part of) the packet it is to dissect. Since after the VLAN dissector there's no other dissector handling the packet data (there's non registered for the ethertype) the info column is left as it was filled in by the VLAN dissector.

What you could do is create a plugin dissector (in Lua would be the easiest, I assume) that registers for your dummy ethertype, which does nothing more than fill the info column with the remaining packet data.

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@Jaap Thank you for the information.

nignasi gravatar imagenignasi ( 2023-03-12 18:03:51 +0000 )edit

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Asked: 2023-03-10 10:45:56 +0000

Seen: 634 times

Last updated: Mar 10 '23