GIF(4) BSD Programmer's Manual GIF(4)NAMEgif - generic tunnel interface
SYNOPSIS
pseudo-device gif [count]
DESCRIPTION
The gif interface is a generic tunnelling pseudo-device for IPv4 and
IPv6. It can tunnel IPv[46] traffic over IPv[46], for a total of four
possible combinations. The behavior of gif is mainly based on RFC 1933
IPv6-over-IPv4 configured tunnel.
A gif interface can be created at runtime using the ifconfig gifN create
command or by setting up a hostname.if(5) configuration file for
netstart(8).
To use gif, the administrator needs to configure the addresses used for
the outer header. This can be done by using ifconfig(8), or through the
SIOCSIFPHYADDR ioctl. The administrator needs to also configure the ad-
dresses used for the inner header, by using ifconfig(8). Note that IPv6
link-local address (those start with fe80::) will be automatically con-
figured whenever possible. One may need to remove any IPv6 link-local ad-
dress manually using ifconfig(8), 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 gif interface.
If plain Ethernet-over-IP is being used, the sysctl(3) variable
net.inet.etherip.allow must be set to 1. This is not necessary in cases
where Ethernet-over-IP is being protected using ipsec(4).
Finally, the gif interface may be used as a bridge(4) member. Ethernet
frames forwarded by the bridge to the gif interface are encapsulated in-
side an IPv4 or IPv6 header (depending on how the interface is config-
ured), with transport protocol number 97 (etherip). IPv4 or IPv6 packets
carrying transport protocol 97 are delivered to the gif 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).
SEE ALSOsysctl(3), inet(4), inet6(4), ipsec(4), ifconfig(8)
R. Gilligan and E. Nordmark, "Transition Mechanisms for IPv6 Hosts and
Routers", RFC 1933, April 1996, ftp://ftp.isi.edu/in-notes/rfc1933.txt.
Sally Floyd, David L. Black, and K. K. Ramakrishnan, IPsec Interactions
with ECN, December 1999, draft-ietf-ipsec-ecn-02.txt.
HISTORY
The gif device first appeared in WIDE hydrangea IPv6 kit.
BUGS
There are many tunnelling protocol specifications, defined differently
from each other. gif may not interoperate with peers which are based on
different specifications, and are picky about outer header fields. For
example, you cannot usually use gif to talk with IPsec devices that use
IPsec tunnel mode.
The current code does not check if the ingress address (outer source
address) configured to gif makes sense. Make sure to configure an address
which belongs to your node. Otherwise, your node will not be able to re-
ceive 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 bridge(4), only one bridge tunnel may
be operational for every pair of source/destination addresses. If more
than one gif interface is configured with the same pair of outer ad-
dresses, the one with the lowest index number will receive all traffic.
MirOS BSD #10-current April 10, 1999 1
