GIF(4) BSD Kernel Interfaces Manual GIF(4)

NAME
     ggiiff - generic tunnel interface

SYNOPSIS
     ppsseeuuddoo-ddeevviiccee ggiiff

DESCRIPTION
     The ggiiff interface is a generic tunnelling pseudo device for IPv4 and
     IPv6.  It can tunnel IPv[46] traffic over IPv[46].  Therefore, there can
     be four possible configurations.  The behavior of ggiiff is mainly based on
     RFC2893 IPv6-over-IPv4 configured tunnel.  On NetBSD, ggiiff can also tunnel
     ISO traffic over IPv[46] using EON encapsulation.

     Each ggiiff interface is created at runtime using interface cloning.  This
     is most easily done with the ifconfig(8) ccrreeaattee command or using the
     gifconfig variable in rc.conf(5).

     To use ggiiff, administrator needs to configure protocol and addresses used
     for the outer header.  This can be done by using gifconfig(8), or
     SIOCSIFPHYADDR ioctl.  Also, administrator needs to configure protocol
     and addresses used for the inner header, by using ifconfig(8).  Note that
     IPv6 link-local address (those start with fe80::) will be automatically
     configured whenever possible.  You may need to remove IPv6 link-local
     address manually using ifconfig(8), when you would like to disable the
     use of IPv6 as inner header (like when you need pure IPv4-over-IPv6 tun-
     nel).  Finally, use routing table to route the packets toward ggiiff inter-
     face.

     ggiiff can be configured to be ECN friendly.  This can be configured by
     IFFLINK1.

   EECCNN ffrriieennddllyy bbeehhaavviioorr
     ggiiff can be configured to be ECN friendly, as described in
     draft-ietf-ipsec-ecn-02.txt.  This is turned off by default, and can be
     turned on by IFFLINK1 interface flag.

     Without IFFLINK1, ggiiff will show a normal behavior, like described in
     RFC2893.  This can be summarized as follows:

           Ingress  Set outer TOS bit to 0.

           Egress   Drop outer TOS bit.

     With IFFLINK1, ggiiff will copy ECN bits (0x02 and 0x01 on IPv4 TOS byte or
     IPv6 traffic class byte) on egress and ingress, as follows:

           Ingress  Copy TOS bits except for ECN CE (masked with 0xfe) from
                    inner to outer.  Set ECN CE bit to 0.

           Egress   Use inner TOS bits with some change.  If outer ECN CE bit
                    is 1, enable ECN CE bit on the inner.

     Note that the ECN friendly behavior violates RFC2893.  This should be
     used in mutual agreement with the peer.

   SSeeccuurriittyy
     Malicious party may try to circumvent security filters by using tunnelled
     packets.  For better protection, ggiiff performs martian filter and ingress
     filter against outer source address, on egress.  Note that mar-
     tian/ingress filters are no way complete.  You may want to secure your
     node by using packet filters.  Ingress filter can be turned off by
     IFFLINK2 bit.

   MMiisscceellllaanneeoouuss
     By default, ggiiff tunnels may not be nested.  This behavior may be modified
     at runtime by setting the sysctl(8) variable net.link.gif.maxnesting to
     the desired level of nesting.  Additionally, ggiiff tunnels are restricted
     to one per pair of end points.  Parallel tunnels may be enabled by set-
     ting the sysctl(8) variable net.link.gif.paralleltunnels to 1.

SEE ALSO
     inet(4), inet6(4), gifconfig(8)

     R. Gilligan and E. Nordmark, "Transition Mechanisms for IPv6 Hosts and
     Routers", RFC2893, August 2000, ftp://ftp.isi.edu/in-notes/rfc2893.txt.

     Sally Floyd, David L. Black, and K. K. Ramakrishnan, IPsec Interactions
     with ECN, December 1999, draft-ietf-ipsec-ecn-02.txt.

HISTORY     The ggiiff device first appeared in WIDE hydrangea IPv6 kit.

BUGS
     There are many tunnelling protocol specifications, defined differently
     from each other.  ggiiff may not interoperate with peers which are based on
     different specifications, and are picky about outer header fields.  For
     example, you cannot usually use ggiiff 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 ggiiff 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 pack-
     ets with a spoofed source address.

     If the outer protocol is IPv4, ggiiff does not try to perform path MTU dis-
     covery for the encapsulated packet (DF bit is set to 0).

     If the outer protocol is IPv6, path MTU discovery for encapsulated packet
     may affect communication over the interface.  The first bigger-than-pmtu
     packet may be lost.  To avoid the problem, you may want to set the inter-
     face MTU for ggiiff to 1240 or smaller, when outer header is IPv6 and inner
     header is IPv4.

     ggiiff does not translate ICMP messages for outer header into inner header.

     In the past, ggiiff had a multi-destination behavior, configurable via
     IFFLINK0 flag.  The behavior was obsoleted and is no longer supported.

     It is thought that this is not actually a bug in gif, but rather lies
     somewhere around a manipulation of an IPv6 routing table.

BSD                             April 10, 1999                             BSD