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How to get the amount of bytes per protocol header?

asked 2018-06-22 08:51:52 +0000

Martijn gravatar image

updated 2018-06-22 09:28:29 +0000

Hi everybody,

For research purposes, I am looking to get the amount of bytes used for each protocol. Unfortunately, the protocol hierarchy all use a cumulative calculation method (size 802.15.4 = size 802.15.4 header + size 6LoWPAN header + ...).

What I want:

  • Frame: 86 bytes
  • Protocol A: 23 bytes
  • Protocol B: 7 bytes
  • Protocol C: 12 bytes
  • Payload: 44 bytes

What wireshark does now:

  • Frame: 86 bytes
  • Protocol A: 86 bytes
  • Protocol B: 63 bytes
  • Protocol C: 56 bytes
  • Payload: 44 bytes

I was wondering I could get this information about bytes per header in a way so I can calculate the total amount of bytes per type of header for a whole pcap file. The information I need seems to be already available per packet on the gui; when you click a header in the tree, the amount of bytes of that header is available in the status bar and the frame bytes window highlights the correct amount of bytes. (screenshot:

I've thought about writing wrapper dissectors in lua for the protocols I use, but I got stuck there trying to tie in the dissectors and retreiving the correct information.

Extra follow-up question:

The packages I examine are 6LoWPAN packets. I would also like to get the amount of bytes actually transmitted. not decompressed. However, the tree headers only give the decompressed amount of bytes. Is this possibile?

With kind regards,


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answered 2018-06-23 19:30:43 +0000

gaddman gravatar image

If the fields already exist, then can you do something like this?

tshark -T fields -e ip.hdr_len -e tcp.hdr_len -e ipv6.hopopts

If that doesn't work and you're comfortable with LUA dissectors, you could use a post-dissector to grab the info you need.

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Asked: 2018-06-22 08:51:52 +0000

Seen: 1,781 times

Last updated: Jun 23 '18