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Version 8 (nion, 02/19/2016 10:49 PM) → Version 9/11 (nion, 02/19/2016 10:49 PM)


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= Wireshark integration

"wireshark":http://www.wireshark.org/
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[http://www.wireshark.org/ wireshark]
is a popular Free Software / Open Source protocol analyzer. Among many
other protocols, it includes dissectors for the GSM Layer 2 (TS 04.06 / LAPDm) and 3 (TS 04.8 04.08 / RR,MM,CC).

There also is a [[GSMTAP]] [wiki:GSMTAP] protocol dissector in recent wireshark versions, which allows
real-time capture and decode of GSM protocol messages encapsulated in a GSMTAP (pseudo-header,
which is in turn encapsulated in UDP and IP).

So if you have a wireshark version with [[GSMTAP]] [wiki:GSMTAP] support (>1.4.0), you can have real-time decode and
trace of GSM protocol messages. You can also [[wireshark|compile wireshark]] [wiki:wireshark compile wireshark] yourself.

The [[OsmocomBB]] [[layer23]] OsmocomBB [wiki:layer23] program sends [[GSMTAP]] [wiki:GSMTAP] packets to the localhost (127.0.0.1) address
of the loopback interface (lo). Please note that the wireshark program is doing passive capture,
i.e. if nothing is listening on the [[GSMTAP]] [wiki:GSMTAP] UDP port (4729), then you will see ICMP port unreachable
messages in addition to the GSMTAP messages. There are two suggested solutions to this:

* Change the IP address to a multicast group like 224.0.0.1 (instead of 127.0.0.1)
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* Run some program that simply opens the UDP port and discards its content, e.g. using {{{nc -u -l -p 4729 > /dev/null}}}

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Screenshot

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[[Image(gsmtap-wireshark.png, 66%)]]
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