The Universal TUN/TAP Driver originated in 2000 as a merger of the corresponding drivers in Solaris, Linux and BSD.[1] The driver continues to be maintained as part of the Linux[2] and FreeBSD[3][4][5] kernels.
Design
TUN and TAP in the network stack
Though both are for tunneling purposes, TUN and TAP can't be used together because they transmit and receive packets at different layers of the network stack. TUN, namely network TUNnel, simulates a network layer device and operates in layer 3 carrying IP packets. TAP, namely network TAP, simulates a link layer device and operates in layer 2 carrying Ethernet frames. TUN is used with routing. TAP can be used to create a user spacenetwork bridge.[2]
Packets sent by an operating system via a TUN/TAP device are delivered to a user space program which attaches itself to the device. A user space program may also pass packets into a TUN/TAP device. In this case the TUN/TAP device delivers (or "injects") these packets to the operating-system network stack thus emulating their reception from an external source.[2]
