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Need to increase TWAMP MBZ integer to 2 Bytes

asked 2023-01-23 18:23:16 +0000

twamp.test.mbz1 MBZ Unsigned integer (1 byte)

Is there any way to edit this filter to support 2 byte field? Routers will insert values greater than 255.

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On Cisco routers, MBZ field is 16 bits

brebelo gravatar imagebrebelo ( 2023-01-23 20:35:33 +0000 )edit

"MBZ" stands for "Must Be Zero"; the only value an MBZ value can have is zero (which is less than 255...), so either this field is not an MBZ field, and its value may have some significance, or those routers have buggy firmware/oftware.

Guy Harris gravatar imageGuy Harris ( 2023-01-24 07:22:59 +0000 )edit

MBZ needs to be corrected and reworded to Session ID. I suppose this is an interpretation of Wireshark which is not correct.

brebelo gravatar imagebrebelo ( 2023-01-24 16:39:27 +0000 )edit

RFC 5357 shows the fields as MBZ.

Chuckc gravatar imageChuckc ( 2023-01-24 16:42:43 +0000 )edit

In Cisco's implementation, the MBZ field is the Session-ID. Without it, the control plane would not be able to differentiate between sessions. All TWAMP sessions originated in the router use the same UDP socket.

I can let the MIG BU know about this RFC discrepancy and get their feedback.

brebelo gravatar imagebrebelo ( 2023-01-24 17:09:31 +0000 )edit

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answered 2023-01-24 02:22:34 +0000

Chuckc gravatar image

updated 2023-01-24 16:25:54 +0000

9592: twamp: test mbz fields are FT_UINT16

Update: this has been merged into the main/master branch.

To test on Windows or Mac, download an automated build or download the source and build on other platforms. (Wireshark-win64-4.1.0rc0-1553-g06fc6483b38f or newer build).

Example capture file is attached to 16264: TWAMP dissector not working.

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Asked: 2023-01-23 18:23:16 +0000

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Last updated: Jan 24 '23