IPv6 in IPv4 (6to4)报文格式

IPv6 in IPv4 (6to4)报文格式
RFC3056定义了6to4隧道。6to4隧道是IETF较为重视并得到深入研究的有广阔应用前景的一种网络过渡机制，可以使连接到纯IPv4网络上的孤立IPv6子网或IPv6站点与其他同类站点在尚未获得纯IPv6连接时彼此间进行通信。
在IPv4网络内可以采用多种路由协议（OSPF、BGP、RIP、IS-IS等），在两个6to4域之间可以通过MP-BGP路由方式实现路由可达。
一、IPv6 in IPv4 (6to4)报文格式

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Version|  IHL  |Type of Service|          Total Length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Identification        |Flags|      Fragment Offset    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Time to Live | Protocol 41   |         Header Checksum       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Source Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Destination Address                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Options                    |    Padding    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            IPv6 header and payload ...              /
     +-------+-------+-------+-------+-------+------+------+

二、IPv6 in IPv4 (6to4)报文示例

Frame 1: 134 bytes on wire (1072 bits), 134 bytes captured (1072 bits)
    Arrival Time: Jun 24, 2008 19:59:07.487397000
    Epoch Time: 1214308747.487397000 seconds
    [Time delta from previous captured frame: 0.000000000 seconds]
    [Time delta from previous displayed frame: 0.000000000 seconds]
    [Time since reference or first frame: 0.000000000 seconds]
    Frame Number: 1
    Frame Length: 134 bytes (1072 bits)
    Capture Length: 134 bytes (1072 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ip:ipv6:icmpv6:data]
    [Coloring Rule Name: ICMP]
    [Coloring Rule String: icmp || icmpv6]
Ethernet II, Src: c2:00:42:02:00:00 (c2:00:42:02:00:00), Dst: c2:01:42:02:00:00 (c2:01:42:02:00:00)
    Destination: c2:01:42:02:00:00 (c2:01:42:02:00:00)
        Address: c2:01:42:02:00:00 (c2:01:42:02:00:00)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..1. .... .... .... .... = LG bit: Locally administered address (this is NOT the factory default)
    Source: c2:00:42:02:00:00 (c2:00:42:02:00:00)
        Address: c2:00:42:02:00:00 (c2:00:42:02:00:00)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..1. .... .... .... .... = LG bit: Locally administered address (this is NOT the factory default)
    Type: IP (0x0800)
Internet Protocol Version 4, Src: 10.0.0.1 (10.0.0.1), Dst: 10.0.0.2 (10.0.0.2)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
    Total Length: 120
    Identification: 0x0009 (9)
    Flags: 0x00
        0... .... = Reserved bit: Not set
        .0.. .... = Don't fragment: Not set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 255
    Protocol: IPv6 (41)
    Header checksum: 0xa751 [correct]
        [Good: True]
        [Bad: False]
    Source: 10.0.0.1 (10.0.0.1)
    Destination: 10.0.0.2 (10.0.0.2)
Internet Protocol Version 6, Src: 2001:db8:0:1::1 (2001:db8:0:1::1), Dst: 2001:db8:0:1::2 (2001:db8:0:1::2)
    0110 .... = Version: 6
        [0110 .... = This field makes the filter "ip.version == 6" possible: 6]
    .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000
        .... 0000 00.. .... .... .... .... .... = Differentiated Services Field: Default (0x00000000)
        .... .... ..0. .... .... .... .... .... = ECN-Capable Transport (ECT): Not set
        .... .... ...0 .... .... .... .... .... = ECN-CE: Not set
    .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000
    Payload length: 60
    Next header: ICMPv6 (0x3a)
    Hop limit: 64
    Source: 2001:db8:0:1::1 (2001:db8:0:1::1)
    Destination: 2001:db8:0:1::2 (2001:db8:0:1::2)
Internet Control Message Protocol v6
    Type: Echo (ping) request (128)
    Code: 0
    Checksum: 0x7e8f [correct]
    Identifier: 0x18dc
    Sequence: 0
    Data (52 bytes)
        Data: 000102030405060708090a0b0c0d0e0f1011121314151617...
        [Length: 52]

三、IPv6 in IPv4 (6to4)协议栈结构

+----------------------+
|     IPv6 payload     |
+----------------------+
|      IPv6 Header     |
+----------------------+
|      IPv4 Header     |
+----------------------+
|    L2 Frame Header   |
+----------------------+