Thursday, July 27, 2017

Remote Capture

Kismet once again supports remote capture in git-master!

Remote packet capture allows multiple systems to report packets back to a single, central Kismet server.  This makes it simple to use light-weight, and usually cheap, embedded devices as remote sensors to expand physical coverage or logical channel coverage.

Remote capture uses the same binaries Kismet uses locally to capture from data sources - for instance, 'kismet_cap_linux_wifi'.  These super-lightweight capture drivers can run on almost any openwrt/lede supported system; the latest version is a 64Kb package, making it plausible to install on almost any device, including limited devices with 4MB of flash.

Remote capture binaries use a fixed amount of RAM - buffers are allocated at the start and are not dynamically adjusted - which means each radio capture uses approximately 4MB of RAM.

Remote capture sources use the same protocol as local, traditional sources - instead of an IPC channel the communication is piped over a TCP socket.  Kismet is able to track what source saw a packet, per-source GPS, using per-source or centralized timestamps, and is able to distribute channels and control channel hopping and other behaviors of remote sources.

More info is in the README:

xx. Remote Packet Capture

    Kismet can capture from a remote source over a TCP connection.

    Kismet remote packet feeds are initiated by the same tools that Kismet uses to
    configure a local source; for example if Kismet is running on a host on IP, to capture from a Linux Wi-Fi device on another device you could

        $ /usr/local/bin/kismet_capture_tools/kismet_cap_linux_wifi \
            --connect --source=wlan1

    Specifically, this uses the kismet_cap_linux_wifi tool, which is by default 
    installed in `/usr/local/bin/kismet_capture_tools/`, to connect to the IP port 3501.

    The --source=... parameter is the same as you would use in a `source=' Kismet
    configuration file entry, or as `-c' to Kismet itself.

    By default, Kismet only allows remote packet connections from the localhost IP; 
    you must either:

    1.  Set up a tunnel, for example using SSH port forwarding, to connect the remote 
        device to the host Kismet is running on.  This is very simple to do, and adds
        security to the remote packet connection:

        $ ssh someuser@ -L 3501:localhost:3501

        Then in another terminal:

        $ /usr/local/bin/kismet_capture_tools/kismet_cap_linux_wifi \
            --connect localhost:3501 --source=wlan1

        The `ssh' command places SSH in the background (using `-f'), connects to 
        the host Kismet is running on, and tunnels port 3501.

        The kismet_cap_linux_wifi command is the same as the first example, but
        connects to localhost:3501 to use the SSH port forwarding.

        Other, more elegant solutions exist for building the SSH tunnel, such 
        as `autossh'.

    2.  Kismet can be configured to accept connections on a specific interface,
        or from all IP addresses, by changing the `remote_capture_listen=' line in


        would enable listening on all interfaces, while


        would enable listening only on the given IP (again using the above example 
        of Kismet running on

        Remote capture *should only be enabled on interfaces on a protected LAN*.

    Additional remote capture arguments

    Kismet capture tools supporting remote capture also support the following options:


        Connects to a remote Kismet server on [host] and port [port].  When using
        `--connect=...' you MUST specify a `--source=...' options

    --source=[source definition]

        Define a source; this is used only in remote connection mode.  The source
        definition is the same as defining a local source for Kismet via `-c' or
        the `source=' config file option.


        By default, a remote source will attempt to reconnect if the connection
        to the Kismet server is lost.


        Places the capture tool in the background and daemonizes it.

A huge thanks to all who support Kismet on Patreon - if you'd like to help, you can become a patron here!

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