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What capture filter will test whether the DSCP value in the IPv4 header is in a particular range?

asked 2020-07-16 15:31:42 +0000

r.grossmann gravatar image

updated 2020-07-17 22:59:44 +0000

Guy Harris gravatar image

Hello,

I just want to capture traffic with specific DSCP Value Range. How can I achieve this? Is there a way to filter for an value range or mask?

I did find the following in the wireshark blog:

ip[1] & 0xfc == 0xb8

This one works, but only for DSCP Value 46. I want to capture only packets with DSCP Value Range 8-23...

I tried it with an edited mask and filter value, but this does not work, only the last original filter for EF...:

ip[1] & 0xe0 == 0x20 or ip[1] & 0xe0 == 0x40 or ip[1] & 0x80 == 0xb8 or ip[1] & 0xfc == 0xb8

So can anyone help me?

Kind regards

Robert

PS: OS Windows 10 Enterprise x64 1909 18363.959 Wireshark Version 3.2.5 (v3.2.5-0-ged20ddea8138)

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answered 2020-07-16 15:51:32 +0000

grahamb gravatar image

updated 2020-07-17 07:48:14 +0000

Untested, but a DSCP range of 8-23 means values of the firstsecond (or index [1]) octet of the IP header are between 0x20 and 0x5C inclusive, so with the appropriate mask gives

(ip[1] & 0xFC >= 0x20) and (ip[1] & 0xFC <= 0x5C)
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thank you, it works! Solution was too easy^^ I'm almost embarrassed to have asked something simple.

r.grossmann gravatar imager.grossmann ( 2020-07-17 06:35:28 +0000 )edit

@r.grossmann Our habit is not to close successfully answered questions, but simply accept the answer by clicking the checkmark to the left of it. I've reopened the question.

grahamb gravatar imagegrahamb ( 2020-07-17 07:46:41 +0000 )edit

okay. sorry for this. I didn't see the check mark on the left side or and other option to accept the answer. I guess i should go to the doctor to check my eyes^^

r.grossmann gravatar imager.grossmann ( 2020-07-17 08:01:42 +0000 )edit

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Asked: 2020-07-16 15:31:42 +0000

Seen: 161 times

Last updated: Jul 17