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I can filter for packet lengths using a display filter containing data.len >= XXX, but I'd really like to use a capture filter for this for efficiency... is there a way to do it?

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Kyle's answer is correct. If you ever do need to use the display filter again, frame.len would be a better choice. "frame" is guaranteed to match every packet. The "data" dissector is usually only called as a last resort, and may not match very many packets. –  Gerald Combs Feb 5 '10 at 19:47
    
cool, thanks for the info. I'll use frame.len from now on. –  paxos1977 Feb 8 '10 at 14:58

2 Answers 2

up vote 5 down vote accepted

As you said in your comment:

greater <length>
less <length>

They also happen to be in this handy tcpdump cheat sheet I have on my wall.

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Wireshark uses the same capture filter syntax as tcpdump, and it doesn't look like that's an option

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+1 for the link to the documentation... but you missed the "greater" option. Apparently, there is also a "len" option. –  paxos1977 Feb 5 '10 at 17:21
    
Wow, yup. You're entirely correct- I was reading it looking for "size" and totally missed "len." Lame :-) –  mfinni Feb 5 '10 at 18:05

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