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GIF(4) Device Drivers Manual GIF(4)

gif
generic tunnel interface

pseudo-device gif

The gif interface is a generic tunnelling pseudo-device. It can tunnel IPv4, IPv6, and MPLS over IPv4 and IPv6, with behavior mainly based on RFC 4213 IPv6-over-IPv4.
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).
The gif interface must be configured with the addresses used for the outer header. This can be done by using ifconfig(8)'s tunnel command (which uses the SIOCSLIFPHYADDR ioctl).
The addresses of the inner header must be configured by using ifconfig(8) in the normal way. The routing table can be used to direct packets toward the gif interface.

sysctl(2), etherip(4), gre(4), inet(4), inet6(4), ipsec(4), hostname.if(5), ifconfig(8), netstart(8)

E. Nordmark and R. Gilligan, Basic Transition Mechanisms for IPv6 Hosts and Routers, RFC 4213, October 2005.
T. Worster, Y. Rekhter, and E. Rosen, Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE), RFC 4023, March 2005.

The gif device first appeared in WIDE hydrangea IPv6 kit.
Previously, gif supported RFC 3378 EtherIP tunnels over bridge(4) interfaces. This is now handled by etherip(4).

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 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.
July 11, 2018 OpenBSD-current