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Erlang TUN/TAP interface
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tunctl is an Erlang API for creating and using TUN/TAP interfaces.



beam needs to have privileges to configure interfaces.

To add cap_net_admin capabilities:

 sudo setcap cap_net_admin=ep /path/to/bin/beam # or beam.smp

To check the privileges:

 getcap cap_net_admin=ep /path/to/bin/beam # or beam.smp

To remove the privileges

 sudo setcap -r cap_net_admin=ep /path/to/bin/beam # or beam.smp

Mac OS X

Requires the tun/tap driver from:

Allow the user running tunctl to call ifconfig using sudo:

sudo visudo
youruser ALL=NOPASSWD: /sbin/ifconfig tap0 *



Tuncer is a stand up guy and just like him, tuncer has your back, cleaning up after you.

create() -> {ok, PID}
create(Device) -> {ok, PID}
create(Device, Options) -> {ok, PID}

    Types   Device = [ string() | binary() ]
            Options = [ Flag ]
            Flag = [ tun | tap | no_pi | one_queue | vnet_hdr | tun_excl ]

    Device is the TUN/TAP interface name. If an interface name is not
    specified, the TUN/TAP driver will choose one (for tap devices,
    starting from "tap0"; for tun devices, beginning from "tun0").

    Options contains a list of flags.

        tun: create a tun interface

        tap: create a tap interface

        no_pi: do not prepend the data with a 4 byte header describing
               the physical interface

    The options default to [tap, no_pi].

destroy(Ref) -> ok

    Types   Ref = pid()

    Remove the TUN/TAP interface.

up(Ref, IPv4) -> ok | {error, posix()}

    Types   Ref = pid()
            IPv4 = list() | tuple()

    Configure a TUN/TAP interface using the default netmask and broadcast
    for the network.

down(Ref) -> ok | {error, posix()}

    Types   Ref = pid()

    Unconfigure a TUN/TAP interface.

persist(Ref, Boolean) -> ok | {error, posix()}

    Types   Ref = pid()
            Boolean = [ true | false ]

    Set the interface to exist after the Erlang process exits.

owner(Ref, Owner) -> ok | {error, posix()}

    Types   Ref = pid()
            Owner = integer()

    Set the uid owning the interface.

group(Ref, Group) -> ok | {error, posix()}

    Types   Ref = pid()
            Group = integer()

    Set the gid owning the interface.

read(Ref, Size) -> {ok, Buf} | {error, posix()}

    Types   Ref = pid()
            Size = integer() Buf = binary()

    Read _Size_ bytes from the interface.

write(Ref, Buf) -> ok | {error, posix()}

    Types   Ref = pid()
            Buf = binary()

    Write _Buf_ to the interface.

devname(Ref) -> Devname

    Types   Devname = binary()

    Returns the TUN/TAP device name.

flags(Ref) -> integer()

    Returns an integer holding the interface creation flags.


tunctl does the actual tun/tap device manipulation. Some functions take a device name, others a file descriptor. It is up to the caller to make sure the file descriptors are closed (the device will disappear after the fd is closed if the device is not persistent).

create() -> {ok, FD, Device}
create(Ifname) -> {ok, FD, Device}
create(Ifname, Flags) -> {ok, FD, Device}

    Types   FD = integer()
            Device = binary()
            Flags = list()

peristFD, Bool) -> ok | {error, posix()}

    Types   FD = integer()
            Bool = true | false

owner(FD, UID) -> ok | {error, posix()}

    Types   FD = integer()
            UID = integer()

group(FD, GID) -> ok | {error, posix()}

    Types   FD = integer()
            UID = integer()

up(Device, IPv4Address) -> ok

    Types   Device = binary()
            IPv$Address = tuple()

down(Device) -> ok

    Types   Device = binary()


1> {ok, Ref} = tuncer:create().

2> tuncer:devname(Ref).

3> tuncer:up(Ref, "").

4> {ok, Buf} = tuncer:read(Ref, 1500).

5> tuncer:read(Ref, Buf).

5> tuncer:destroy(Ref).


  • on Linux, the TUNSETIFF ioctl request to create the interface requires CAP_NET_ADMIN privileges. Look at moving the interface creation into the procket setuid binary for OSes that use the multiplexing dev.

  • compat for other BSDs: /dev/tun multiplex dev, probably the same issue with interface creation

  • make sure tuncer can never leak file descriptors

  • add {active,true} mode using open_port/2

  • add support for tun filtering

  • support for setting pointopoint

  • IPv6 addresses on tun devices

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