ICMPv6邻居通告NA（Neighbor Advertisement）消息
ICMPv6邻居通告NA（Neighbor Advertisement）消息是IPv6节点对ICMPv6邻居请求NS（Neighbor Solicitation）消息的响应，同时IPv6节点在链路层变化时也可以主动发送NA消息。
一、ICMPv6邻居通告报文格式
+0-------7-------15---------------31
| Type | Code | Checksum |
+----------------------------------
|R|S|O| Reserved |
+----------------------------------
| Target Address |
+----------------------------------
| Options... |
+---------------------------------+
二、ICMPv6邻居通告报文格式解释
| 字段 | 长度 | 含义 |
|---|---|---|
| Type | 1字节 | 消息类型，此处值为136。 |
| Code | 1字节 | 该ICMPv6差错报文的始发者必须将该字段置为0，且接收端忽略该字段。 |
| Checksum | 2字节 | 用来在ICMPv6报文中检验数据和部分IPv6首部的完整性。 |
| R | 1比特 | 路由器标记。当置1时，R位指出发送者是路由器。R位由Neighbor Unreachability Detection使用，用于检测改变为主机的路由器。 |
| S | 1比特 | 请求标记。当置1时，S位指出通告被发送以响应来自目的地地址的Neighbor Solicitation。S位用作Neighbor Unreachability Detection的可达性确认。在多播通告和非请求单播通告中置0。 |
| O | 1比特 | 替代标记。替代标志，1表示通告中的信息替代缓存，如更新链路层地址时，对于任播的回应则不应置位。在针对任播地址的请求通告中，以及在请求的前缀通告中它不能被置1。在其他请求通告中和在非请求通告中它应当被置1。 |
| Reserved | 29比特 | 29位未使用字段。它必须由发送者初始化为0，接收者必须忽略它。 |
| Target Address | 16字节 | 对于请求的通告，是在Neighbor Solicitation消息(该消息催促这个通告)中的Target Address字段。对于非请求通告，是其链路层地址已经改变的地址。Target Address必须不是多播地址。 |
| Options | 可变 | 选项：
|
三、ICMPv6邻居通告报文示例
Frame 1: 86 bytes on wire (688 bits), 86 bytes captured (688 bits)
Arrival Time: Sep 25, 2012 11:24:31.033087000
Epoch Time: 1348543471.033087000 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: 86 bytes (688 bits)
Capture Length: 86 bytes (688 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ipv6:icmpv6]
[Coloring Rule Name: ICMP]
[Coloring Rule String: icmp || icmpv6]
Ethernet II, Src: RealtekS_88:5a:81 (00:e0:4c:88:5a:81), Dst: 00:46:4b:d8:28:c7 (00:46:4b:d8:28:c7)
Destination: 00:46:4b:d8:28:c7 (00:46:4b:d8:28:c7)
Address: 00:46:4b:d8:28:c7 (00:46:4b:d8:28:c7)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Source: RealtekS_88:5a:81 (00:e0:4c:88:5a:81)
Address: RealtekS_88:5a:81 (00:e0:4c:88:5a:81)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Type: IPv6 (0x86dd)
Internet Protocol Version 6, Src: 2008::230 (2008::230), Dst: fe80::246:4bff:fed8:28c7 (fe80::246:4bff:fed8:28c7)
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: 32
Next header: ICMPv6 (0x3a)
Hop limit: 255
Source: 2008::230 (2008::230)
Destination: fe80::246:4bff:fed8:28c7 (fe80::246:4bff:fed8:28c7)
[Destination SA MAC: 00:46:4b:d8:28:c7 (00:46:4b:d8:28:c7)]
Internet Control Message Protocol v6
Type: Neighbor Advertisement (136)
Code: 0
Checksum: 0x34e3 [correct]
Flags: 0xe0000000
1... .... .... .... .... .... .... .... = Router: Set
.1.. .... .... .... .... .... .... .... = Solicited: Set
..1. .... .... .... .... .... .... .... = Override: Set
...0 0000 0000 0000 0000 0000 0000 0000 = Reserved: 0
Target Address: 2008::230 (2008::230)
ICMPv6 Option (Target link-layer address : 00:e0:4c:88:5a:81)
Type: Target link-layer address (2)
Length: 1 (8 bytes)
Link-layer address: RealtekS_88:5a:81 (00:e0:4c:88:5a:81)
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