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 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).
Building from source¶
In order to be able to dissect all protocols relevant for Osmocom, you will need to install the git version of wireshark (as of writing, the latest stable is 2.6 and it does not yet have support for GSUP for example). See #2537 for an effort to ship Debian binary packages with Osmocom patches applied.
|Fedora 28||@development-tools cmake c-ares-devel glib2-devel libcap-devel libpcap-devel lua libmaxminddb-devel qt5-qtmultimedia-devel qt5-qttools-devel qt5-qtsvg-devel gnutls-devel libssh-devel libgcrypt-devel flex byacc|
Building and installing¶
$ git clone --depth=1 "https://code.wireshark.org/review/wireshark.git" $ cd wireshark $ mkdir -p cmake-build-dir $ cd cmake-build-dir $ cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr/local $ make $ sudo make install $ sudo setcap 'CAP_NET_RAW+eip CAP_NET_ADMIN+eip' /usr/local/bin/dumpcap $ sudo ldconfig
There are various preferences that need to be set for optimal decoding of the protocols we're interested in:
gsm_abis_oml.oml_dialect: ip.access amr.dynamic.payload.type: 126 fr.encap: GPRS Network Service iuup.dynamic.payload.type: 103 lapd.use_gsm_sapi_values: TRUE gsm_abis_rsl.use_ipaccess_rsl: TRUE sccp.default_payload: bssap gprs-ns.udp.port: 2157,19999,23020,23000
One way to apply these settings, is closing wireshark and copying them at the end of
Common display filters¶
gsm_abis_oml || gsm_abis_rsl || bssap || mgcp || gsup || rtp || rtcp ipaccess || sccp || sctp gprs_ns || gtp gsmtap || gsmtap_log gsm_ipa
Workaround for "ICMP port unreachable" messages¶The OsmocomBB layer23 program sends 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 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 188.8.131.52 (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