interface is a generic tunnelling pseudo-device for IPv4 and IPv6.
It can tunnel IPv traffic over IPv, for a total of four
The behavior of
is mainly based on RFC 1933 IPv6-over-IPv4 configured tunnel.
interface can be created at runtime using the
command or by setting up a
configuration file for
the administrator needs to configure the addresses used for the outer header.
This can be done by using
or through the
The administrator needs to also configure the addresses used for the
inner header, by using
Note that IPv6 link-local address
(those start with fe80::)
will be automatically configured whenever possible.
One may need to remove any IPv6 link-local address manually using
to disable the use of IPv6 as inner header
(e.g., when a pure IPv4-over-IPv6 tunnel is required).
Also, the routing table may be used to route the packets toward the
If plain Ethernet-over-IP is being used,
must be set to 1.
This is not necessary in cases where Ethernet-over-IP is being
interface may be used as a
Ethernet frames forwarded by the bridge to the
interface are encapsulated inside an IPv4 or IPv6 header (depending on
how the interface is configured), with transport protocol number 97
IPv4 or IPv6 packets carrying transport protocol 97 are delivered to
interface whose "physical" addresses match the source/destination
addresses of the packet (the source address of the packet must match
the destination "physical" address, and vice versa).
.%A R. Gilligan
.%A E. Nordmark
.%B RFC 1933
.%T Transition Mechanisms for IPv6 Hosts and Routers
.%D April 1996
.%A Sally Floyd
.%A David L. Black
.%A K. K. Ramakrishnan
.%T IPsec Interactions with ECN
.%D December 1999
device first appeared in WIDE hydrangea IPv6 kit.
There are many tunnelling protocol specifications,
defined differently from each other.
may not interoperate with peers which are based on different specifications,
and are picky about outer header fields.
For example, you cannot usually use
to talk with IPsec devices that use IPsec tunnel mode.
The current code does not check if the ingress address
(outer source address)
Make sure to configure an address which belongs to your node.
Otherwise, your node will not be able to receive packets from the peer,
and your node will generate packets with a spoofed source address.
If the outer protocol is IPv6, path MTU discovery for encapsulated packet
may affect communication over the interface.
When used in conjunction with the
only one bridge tunnel may be operational for every pair of
If more than one
interface is configured with the same pair of outer addresses, the
one with the lowest index number will receive all traffic.