using tun/tap device the erlang way

[benoitc]

I am interresting to setup such tunnel, but how would you open such device from erlang and read it? For example if you want to accept connections for an http server over it. Any hint is welcome :)

[colrack]

Hi Benoit
You can open tun/tap devices in active or passive mode with tuncer:create.
There is a C port that opens the tun/tap sockets since the vm is not capable of opening them.
The port opens the socket and then passes it to the vm (this is done in procket).
When you open such a socket you are dealing with raw IP packets or Ethernet frames; in the former case you opened a tun device, in the latter a tap device.
Implementing an http server on top of a tun device is not trivial since you need userspace TCP stack;
implementing it on top of layer 2 is even harder!
The main use case for tun/tap devices is to leverage the kernel net stack from userspace.
Usually you set up a "tunnel" on top of transport protocols; eg, you open a UDP or TCP socket and you send IP or Ethernet packets over it (the packets you read from the tun socket); on the other side, you receive packets via UDP/TCP and you write them to the tun/tap device and let the kernel deal with them.
Hope this helps

[msantos]

Hey @benoitc ! @colrack's answer is excellent and pretty much covers
everything.

Basically the erlang process creates and attaches to a virtual interface
and receives either ethernet (tap interface) or ip (tun interface)
frames. Imagine we have 2 computers on different networks, assigned
10.10.10.10 and 10.10.20.10:

host1: 192.168.100.1/24 tun0 -- erlang -- 10.10.10.10/eth0 ---- host2: 10.10.20.10/eth0 -- erlang tun0 192.168.100.2/24                                           

Any packets on host1 destined for 192.168.100.2 would be routed via
tun0. The erlang process would receive the frame and could modify, drop
or forward it. How the erlang process encodes and forwards the frame is
arbitrary: for example, it could base64 encode the frame and send it as an
HTTP body to 10.10.20.10 or send it over the erlang distribution protocol.

The erlang process can also handle the frames directly. In that case,
as @colrack mentioned, the process could implement a UDP/IP or TCP/IP stack.

If anything isn't clear, feel free to ask questions!