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Hi. I have a trace of RADIUS accounting requests/responses where I accidentally stumbled upon an event that I happened to be looking for. The pattern I see is a NAD sending multiple RADIUS accounting requests that never received an accounting response. The nature of my problem I am trying to solve is such that I need a display filter to help me find these events. Is there a way I construct a display filter to find RADIUS accounting requests that never received a response?

asked 27 Aug '15, 12:52

smp's gravatar image

smp
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accept rate: 0%


Can't you just do:

radius.req && !radius.rspframe

I haven't tried it, but it looks like it should work. (note that if using tshark, it will require a "-2" double pass)

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answered 28 Aug '15, 06:14

Hadriel's gravatar image

Hadriel
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accept rate: 18%

Hi, thanks for the response. What I am looking for is to isolate radius packets that never receive a radius response. Your filter seems to display /all/ the radius request packets, which admittedly includes the one I am interested it. But it doesn't filter out all the requests that /do/ receive a response.

Sorry if that wasn't clear in my original post.

(28 Aug '15, 06:34) smp

When you look at the RADIUS request packets that do have responses, do they not have something in the Packet Details display tree that says something like "[The response to this request is in frame ...]"?

(28 Aug '15, 06:51) Hadriel

Yes, they do.

(28 Aug '15, 07:00) smp

Huh, well then that display filter should have worked I would think. So I just tried it on a sample capture, and it worked - only RADIUS request packets without a response are shown. Are you sure you did the full filter: "radius.req && !radius.rspframe"?

(28 Aug '15, 07:05) Hadriel

Thanks for your continued assistance. radius.req && radius.rspframe == 0 removes all the frames.

(28 Aug '15, 07:10) smp

Are you doing this in Wireshark, or tshark? And what exactly are you doing to apply the display filter?

(28 Aug '15, 07:11) Hadriel

OK good - "radius.req && radius.rspframe == 0" should have filtered them all. I was just trying to debug why "radius.req && !radius.rspframe" isn't working, because it should work.

(28 Aug '15, 07:12) Hadriel

I just took another trace and used your "radius.req && !radius.rspframe" filter, and as I study it more closely, it /is/ working. I think the problem is just that there are more packets than I intuitively expected.

Sorry about my laziness which caused you extra work. This is what I needed - thanks a lot!!!

(28 Aug '15, 07:24) smp

If this solved your problem, please accept the answer.

(28 Aug '15, 07:25) Kurt Knochner ♦

Be careful when filtering RADIUS packets. The current dissector does not do a very good job at matching up requests and responses, often incorrectly tagging packets as duplicates when they are not. See bug 4096 (and bug 5720 , which was marked as a duplicate of bug 4096).

(28 Aug '15, 07:48) cmaynard ♦♦
1

Then to be safe, you could make it "(radius.req && !radius.rspframe) || radius.dup" to see only requests without a response and all duplicate RADIUS messages; or "(radius.req && !radius.rspframe) || radius.rsp.dup" to see only requests without a response and all duplicate responses, in case a duplicate response was incorrectly associated with the wrong request.

(28 Aug '15, 08:21) Hadriel
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answered 28 Aug '15, 04:48

Kurt%20Knochner's gravatar image

Kurt Knochner ♦
24.8k1039237
accept rate: 15%

Learning MATE seems to be something that will take me quite a bit of time, given my skillset. Not sure if I will be successful or not. But given your forum reputation, I think it's safe to assume this will probably do what I need. Thanks a lot for the references - I have never heard of MATE until now.

(28 Aug '15, 06:36) smp
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question asked: 27 Aug '15, 12:52

question was seen: 5,543 times

last updated: 28 Aug '15, 08:21

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