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28 .\" $Id: gif.4,v 1.2 1999/09/29 15:36:17 itojun Exp $
37 .Tn Generic tunnel interface
39 .Cd "pseudo-device gif 4"
43 interface is a generic tunnelling pseudo device for IPv4 and IPv6.
44 It can tunnel IPv[46] traffic over IPv[46].
45 Therefore, there can be four possible configurations.
48 is mainly based on RFC1933 IPv6-over-IPv4 configured tunnel.
52 administrator needs to configure protocol and addresses used for the outer
54 This can be done by using
59 Also, administrator needs to configure protocol and addresses used for the
60 inner header, by using
62 Note that IPv6 link-local address
63 .Pq those start with Li fe80::
64 will be automatically configured whenever possible.
65 You may need to remove IPv6 link-local address manually using
67 when you would like to disable the use of IPv6 as inner header
68 .Pq like when you need pure IPv4-over-IPv6 tunnel .
69 Finally, use routing table to route the packets toward
74 interface can be configued to perform bidirectional tunnel, or
75 multi-destination tunnel.
81 can be configured to be ECN friendly.
82 This can be configured by
85 .Ss Bidirectional and multi-destination mode
88 implements bidirectional tunnel.
90 should configure a tunnel ingress point
97 interface will tunnel to only a single tunnel endpoint,
98 and accept from only a single tunnel endpoint.
99 Source and destination address for outer IP header is always the
100 ingress and the egress point configued by
107 can be configured to implement multi-destination tunnel.
110 it is able to configure egress point to IPv4 wildcard address
112 or IPv6 unspecified address
114 In this case, destination address for the outer IP header is
115 determined based on the routing table setup.
118 interface can tunnel to multiple destinations.
121 will accept tunneled traffic from any outer source address.
125 interface from the inbound tunneled traffic,
126 bidirectional mode interface is preferred than multi-destination mode interface.
127 For example, if you have the following three
129 interfaces on node A, tunneled traffic from C to A will match the second
131 interface, not the third one.
132 .Bl -bullet -compact -offset indent
134 bidirectional, A to B
136 bidirectional, A to C
138 multi-destination, A to any
141 Please note that multi-destination mode is far less secure
142 than bidirectional mode.
143 Multi-destination mode
145 can accept tunneled packet from anybody,
146 and can be attacked from a malicious node.
148 .Ss ECN friendly behavior
150 can be configured to be ECN friendly, as described in
151 .Dv draft-ipsec-ecn-00.txt .
152 This is turned off by default, and can be turned on by
159 will show a normal behavior, like described in RFC1933.
160 This can be summarized as follows:
161 .Bl -tag -width "Ingress" -offset indent
177 on IPv4 TOS byte or IPv6 traffic class byte
179 on egress and ingress, as follows:
180 .Bl -tag -width "Ingress" -offset indent
182 Copy TOS bits except for ECN CE
192 Use inner TOS bits with some change.
193 If outer ECN CE bit is
195 enable ECN CE bit on the inner.
198 Note that the ECN friendly behavior violates RFC1933.
199 This should be used in mutual agreement with the tunnel endpoint.
201 .Ss Backward compatibility
203 interface will capture packets toward IPv4-in-IPv4 tunnel,
204 which has been used by
206 multicast tunnel device
207 .Pq used in MBone community .
208 For compatibility, IPv4-in-IPv4 traffic will be matched to
210 interfaces first, and then sent to
212 if no match is found.
223 .%A K. K. Ramakrishnan
224 .%T "IPsec Interactions with ECN"
226 .%O http://www.aciri.org/floyd/papers/draft-ipsec-ecn-00.txt
232 device first appeared in WIDE hydrangea IPv6 kit.