= Wireshark integration =

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

The OsmocomBB [wiki:layer23] program sends [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 [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) * Run some program that simply opens the UDP port and discards its content, e.g. using {{{nc -u -l -p 4729 > /dev/null}}}

Image(gsmtap-wireshark.png, 66%)