On a node, there exist different network devices. They can be collected in classes
5.1.2. Virtually bounded
Virtually bounded interfaces always need special support
18.104.22.168. IPv6-in-IPv4 tunnel interfaces
These interfaces are normally named sitx. The name sit is a shortcut for Simple Internet Transition. This device has the capability to encapsulate IPv6 packets into IPv4 ones and tunnel them to a foreign endpoint.
sit0 has a special meaning and cannot be used for dedicated tunnels.
22.214.171.124. PPP interfaces
PPP interfaces get their IPv6 capability from an IPv6 enabled PPP daemon.
126.96.36.199. ISDN HDLC interfaces
IPv6 capability for HDLC with encapsulation ip is already built-in in the kernel
188.8.131.52. ISDN PPP interfaces
ISDN PPP interfaces (ippp) aren't IPv6 enabled by kernel. Also there are also no plans to do that because in kernel 2.5.+ they will be replaced by a more generic ppp interface layer.
184.108.40.206. SLIP + PLIP
Like mentioned earlier, this interfaces don't support IPv6 transport (sending is OK, but dispatching on receiving don't work).
220.127.116.11. Ether-tap device
Ether-tap devices are IPv6-enabled and also stateless configured. For use, the module "ethertap" has to be loaded before.
18.104.22.168. tun devices
Currently not tested by me.
01/2002: Aren't currently supported by vanilla kernel, supported by USAGI extension
Did I forget an interface?...