1.\" Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the project nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" $Id: gif.4,v 1.2 1999/09/29 15:36:17 itojun Exp $ 29.\" $FreeBSD$ 30.\" 31.Dd April 10, 1999 32.Dt GIF 4 33.Os 34.Sh NAME 35.Nm gif 36.Nd 37.Tn Generic tunnel interface 38.Sh SYNOPSIS 39.Cd "pseudo-device gif 4" 40.Sh DESCRIPTION 41The 42.Nm 43interface is a generic tunnelling pseudo device for IPv4 and IPv6. 44It can tunnel IPv[46] traffic over IPv[46]. 45Therefore, there can be four possible configurations. 46The behavior of 47.Nm 48is mainly based on RFC1933 IPv6-over-IPv4 configured tunnel. 49.Pp 50To use 51.Nm gif , 52administrator needs to configure protocol and addresses used for the outer 53header. 54This can be done by using 55.Xr gifconfig 8 , 56or 57.Dv SIOCSIFPHYADDR 58ioctl. 59Also, administrator needs to configure protocol and addresses used for the 60inner header, by using 61.Xr ifconfig 8 . 62Note that IPv6 link-local address 63.Pq those start with Li fe80:: 64will be automatically configured whenever possible. 65You may need to remove IPv6 link-local address manually using 66.Xr ifconfig 8 , 67when you would like to disable the use of IPv6 as inner header 68.Pq like when you need pure IPv4-over-IPv6 tunnel . 69Finally, use routing table to route the packets toward 70.Nm 71interface. 72.Pp 73.Nm 74interface can be configued to perform bidirectional tunnel, or 75multi-destination tunnel. 76This is controlled by 77.Dv IFF_LINK0 78interface flag. 79Also, 80.Nm 81can be configured to be ECN friendly. 82This can be configured by 83.Dv IFF_LINK1 . 84.\" 85.Ss Bidirectional and multi-destination mode 86Usually, 87.Nm 88implements bidirectional tunnel. 89.Xr gifconfig 8 90should configure a tunnel ingress point 91.Pq this node 92and an egress point 93.Pq tunnel endpoint , 94and 95one 96.Nm 97interface will tunnel to only a single tunnel endpoint, 98and accept from only a single tunnel endpoint. 99Source and destination address for outer IP header is always the 100ingress and the egress point configued by 101.Xr gifconfig 8 . 102.Pp 103With 104.Dv IFF_LINK0 105interface flag, 106.Nm 107can be configured to implement multi-destination tunnel. 108With 109.Dv IFF_LINK0 , 110it is able to configure egress point to IPv4 wildcard address 111.Pq Nm 0.0.0.0 112or IPv6 unspecified address 113.Pq Nm 0::0 . 114In this case, destination address for the outer IP header is 115determined based on the routing table setup. 116Therefore, one 117.Nm 118interface can tunnel to multiple destinations. 119Also, 120.Nm 121will accept tunneled traffic from any outer source address. 122.Pp 123When finding a 124.Nm gif 125interface from the inbound tunneled traffic, 126bidirectional mode interface is preferred than multi-destination mode interface. 127For example, if you have the following three 128.Nm 129interfaces on node A, tunneled traffic from C to A will match the second 130.Nm 131interface, not the third one. 132.Bl -bullet -compact -offset indent 133.It 134bidirectional, A to B 135.It 136bidirectional, A to C 137.It 138multi-destination, A to any 139.El 140.Pp 141Please note that multi-destination mode is far less secure 142than bidirectional mode. 143Multi-destination mode 144.Nm 145can accept tunneled packet from anybody, 146and can be attacked from a malicious node. 147.Pp 148.Ss ECN friendly behavior 149.Nm 150can be configured to be ECN friendly, as described in 151.Dv draft-ipsec-ecn-00.txt . 152This is turned off by default, and can be turned on by 153.Dv IFF_LINK1 154interface flag. 155.Pp 156Without 157.Dv IFF_LINK1 , 158.Nm 159will show a normal behavior, like described in RFC1933. 160This can be summarized as follows: 161.Bl -tag -width "Ingress" -offset indent 162.It Ingress 163Set outer TOS bit to 164.Dv 0 . 165.It Egress 166Drop outer TOS bit. 167.El 168.Pp 169With 170.Dv IFF_LINK1 , 171.Nm 172will copy ECN bits 173.Po 174.Dv 0x02 175and 176.Dv 0x01 177on IPv4 TOS byte or IPv6 traffic class byte 178.Pc 179on egress and ingress, as follows: 180.Bl -tag -width "Ingress" -offset indent 181.It Ingress 182Copy TOS bits except for ECN CE 183.Po 184masked with 185.Dv 0xfe 186.Pc 187from 188inner to outer. 189set ECN CE bit to 190.Dv 0 . 191.It Egress 192Use inner TOS bits with some change. 193If outer ECN CE bit is 194.Dv 1 , 195enable ECN CE bit on the inner. 196.El 197.Pp 198Note that the ECN friendly behavior violates RFC1933. 199This should be used in mutual agreement with the tunnel endpoint. 200.Pp 201.Ss Backward compatibility 202.Nm 203interface will capture packets toward IPv4-in-IPv4 tunnel, 204which has been used by 205.Xr vif 4 206multicast tunnel device 207.Pq used in MBone community . 208For compatibility, IPv4-in-IPv4 traffic will be matched to 209.Nm 210interfaces first, and then sent to 211.Xr vif 4 212if no match is found. 213.\" 214.Sh SEE ALSO 215.Xr inet 4 , 216.Xr inet6 4 , 217.Xr vif 4 , 218.Xr gifconfig 8 , 219RFC1933 220.Rs 221.%A Sally Floyd 222.%A David L. Black 223.%A K. K. Ramakrishnan 224.%T "IPsec Interactions with ECN" 225.%D February 1999 226.%O http://www.aciri.org/floyd/papers/draft-ipsec-ecn-00.txt 227.Re 228.\" 229.Sh HISTORY 230The 231.Nm 232device first appeared in WIDE hydrangea IPv6 kit. 233