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How do I only dissect packets within a range of IP addresses but any port?

asked 2019-01-04 10:19:32 +0000

JCAMP gravatar image

I'd like to dissect UDP packets whose destination IP address is within a range of IP addresses. I seem to be able to have my dissector working on a particular port using dissector_add_uint("udp.port", PORT, pro_handle) but I'd like to dissect UDP packets to any port, but with a particular IP address.

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answered 2019-01-04 21:47:34 +0000

cmaynard gravatar image

I think what you'll need to do is to register your dissector a heuristic dissector. This basically means that your dissector will be handed every UDP packet that hasn't been claimed by another dissector [NOTE]. Your dissector will have to heuristically determine whether the packet is actually intended for your dissector or not and dissect it if it is or reject it if it isn't so that another dissector gets a chance to dissect it.

Refer to doc/README.heuristic as well as the many built-in Wireshark dissectors for examples on how to use this. One rather simple one is packet-wol.c.

[Note] Unless the UDP Try heuristic sub-dissectors first option is selected, in which case your dissector will get a chance to claim it before any other registered dissectors, although it's not entirely clear what the heuristic order will be, so it's possible that another heuristic dissector could still claim it, in which case heuristics need to be improved by the dissector that incorrectly claimed it or that dissector may need to be disabled altogether in order for your dissector to get a chance to claim the packet.

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Thank you. Do you know how to get the destination IP address from the packet within the dissector? I've tried many approaches that other dissectors use but can't get any of them to work. The IP address in an integer form is preferred.

JCAMP gravatar imageJCAMP ( 2019-01-07 15:31:00 +0000 )edit

Please ask this in a new question. Asking additional questions as comments in other questions means these questions can get buried and be harder for others to find. It also isn't relevant to the original question asked and answered and which can be accepted if it has indeed answered your question. That way, others know as well, both in the case of folks looking to help answer questions and those looking for answers to the same or similar questions themselves.

cmaynard gravatar imagecmaynard ( 2019-01-07 15:49:37 +0000 )edit

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Asked: 2019-01-04 10:19:32 +0000

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Last updated: Jan 04 '19