用途说明
IIH：用于建立和维持邻接关系：
1）在广播网络中：Level-1 IS-IS Router 使用 Level-1 LAN IIH； Level-2 IS-IS Router 使用 Level-2 LAN IIH；
2）在点到点网络中，则使用 P2P IIH；
报文结构
这些字段：属于 PDU Specific Header 部分；处于 PDU Common Header 与 Variable Length Fidleds 之间；
Reserved/Circuit Type：表示路由器的类型（0x01表示L1；0x10表示L2；0x11表示L1/L2; ）；
Source ID：发出 Hello 报文的路由器的 System ID；
Holding Time： 保持时间。在此时间内如果没有收到邻接发来的 Hello 报文，则中止已建立的邻接关系；
R：保留位；
Priority：选举 DIS 的优先级，7bit，0～127。数值越大，优先级越高；
1）该字段只在 MA Network 中的Hello消息（LAN IIH 消息）携带；
2）P2P Network 的 Hello 消息（P2P IIH 消息）没有此字段，也没有此字段之前的R保留位；
LAN ID / System ID / Designated IS，是 DIS 的 ID（<System ID>.<PseudoNode ID>）；
1）该字段只在 MA Network 中的 Hello 消息（LAN IIH 消息）携带；
2）在 P2P Network 的 Hello 消息（P2P IIH消息）没有此字段；
Local Circuit ID：本地链路 ID；
1）该字段只在 P2P Network 的 Hello 消息（P2P IIH 消息）携带；
2）在 MA Network 中的 Hello 消息（LAN IIH消息）没有此字段；
报文示例
Frame 368: 1514 bytes on wire (12112 bits), 1514 bytes captured (12112 bits) on interface -, id 0
IEEE 802.3 Ethernet
Logical-Link Control
ISO 10589 ISIS InTRA Domain Routeing Information Exchange Protocol
ISIS HELLO
.... ..11 = Circuit type: Level 1 and 2 (0x3)
0000 00.. = Reserved: 0x00
SystemID {Sender of PDU}: 0000.0000.7777
Holding timer: 9
PDU length: 1497
.100 0000 = Priority: 64
0... .... = Reserved: 0
SystemID {Designated IS}: 0000.0000.7777.02
Area address(es) (t=1, l=4)
Type: 1
Length: 4
Area address (3): 49.0003
IS Neighbor(s) (t=6, l=6)
IP Interface address(es) (t=132, l=4)
Protocols Supported (t=129, l=1)
Restart Signaling (t=211, l=3)
Multi Topology (t=229, l=2)
Padding (t=8, l=255)
Padding (t=8, l=255)
Padding (t=8, l=255)
Padding (t=8, l=255)
Padding (t=8, l=255)
Padding (t=8, l=151)
ISIS HELLO, IPv6
Frame 1209: 1514 bytes on wire (12112 bits), 1514 bytes captured (12112 bits) on interface -, id 0
IEEE 802.3 Ethernet
Destination: ISIS-all-level-1-IS's (01:80:c2:00:00:14)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
Source: 38:39:cc:01:01:00 (38:39:cc:01:01:00)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
Length: 1500
[Stream index: 6]
Logical-Link Control
DSAP: ISO Network Layer (0xfe)
1111 111. = SAP: ISO Network Layer
.... ...0 = IG Bit: Individual
SSAP: ISO Network Layer (0xfe)
1111 111. = SAP: ISO Network Layer
.... ...0 = CR Bit: Command
Control field: U, func=UI (0x03)
000. 00.. = Command: Unnumbered Information (0x00)
.... ..11 = Frame type: Unnumbered frame (0x3)
ISO 10589 ISIS InTRA Domain Routeing Information Exchange Protocol
Intradomain Routing Protocol Discriminator: ISIS (0x83)
Length Indicator: 27
Version/Protocol ID Extension: 1
ID Length: 6
000. .... = Reserved: 0x0
...0 1111 = PDU Type: L1 HELLO (15)
Version: 1
Reserved: 0
Maximum Area Addresses: 3
ISIS HELLO
.... ..11 = Circuit type: Level 1 and 2 (0x3)
0000 00.. = Reserved: 0x00
SystemID {Sender of PDU}: 0000.0000.1111
Holding timer: 30
PDU length: 1497
.100 0000 = Priority: 64
0... .... = Reserved: 0
SystemID {Designated IS}: 0000.0000.1111.01
Area address(es) (t=1, l=4)
Type: 1
Length: 4
Area address (3): 49.0001
Protocols Supported (t=129, l=1)
Type: 129
Length: 1
NLPID: IPv6 (0x8e)
NLPID: 0x8e
IPv6 Interface address(es) (t=232, l=16)
Type: 232
Length: 16
IPv6 interface address: fe80::3a39:ccff:fe01:100
IPv6 Global Interface Address (t=233, l=16)
Type: 233
Length: 16
IPv6 Global interface address: 2000:12::1
Multi Topology (t=229, l=2)
Type: 229
Length: 2
IPv4 Unicast Topology (0x000)
Restart Signaling (t=211, l=3)
Type: 211
Length: 3
Restart Signaling Flags: 0x00
.... .0.. = Suppress Adjacency: False
.... ..0. = Restart Acknowledgment: False
.... ...0 = Restart Request: False
Padding (t=8, l=255)
Type: 8
Length: 255
Padding (t=8, l=255)
Type: 8
Length: 255
Padding (t=8, l=255)
Type: 8
Length: 255
Padding (t=8, l=255)
Type: 8
Length: 255
Padding (t=8, l=255)
Type: 8
Length: 255
Padding (t=8, l=129)
Type: 8
Length: 129