IS-IS 网络协议 LSP消息
IS-IS链路状态报文LSP（Link State PDUs）用于交换链路状态信息。LSP分为两种：Level–1 LSP和Level–2 LSP。Level–1 LSP由Level-1路由器传送，Level–2 LSP由Level-2路由器传送，Level-1-2路由器则可传送以上两种LSP。两类LSP有相同的报文格式。
一、L1/L2 LSP报文格式
+----------------------------------------------+------------
| Intradomain Routing Protocol Discriminator | |
+----------------------------------------------+ |
| Length Indicator | |
+----------------------------------------------+ |
| Version/Protocol ID Extension | |
+----------------------------------------------+ |
| ID Length | PDU
+----------------------------------------------+ Common
| R | R | R | PDU Type | Header
+----------------------------------------------+ |
| Version | |
+----------------------------------------------+ |
| Reserved | |
+----------------------------------------------+ |
| Maximum Area Address | |
+----------------------------------------------+------------
| PDU Length | |
+----------------------------------------------+ |
| Remaining Lifetime | |
+----------------------------------------------+ |
| LSP ID | PDU
+----------------------------------------------+ Specific
| Sequency Number | Header
+----------------------------------------------+ |
| Checksum | |
+----------------------------------------------+ |
| P | ATT | OL | IS Type | |
+----------------------------------------------+------------
| Variable Length Fields(CLV) |
+----------------------------------------------+二、L1/L2 LSP报文格式各字段含义
| 字段 | 长度 | 含义 |
|---|---|---|
| Intradomain Routing Protocol Discriminator | 1字节 | 域内路由选择协议鉴别符，设置为0x83。 |
| Length Indicator | 1字节 | PDU头部的长度（包括通用头部和专用头部），以字节为单位。 |
| Version/Protocol ID Extension | 1字节 | 版本/协议标识扩展，设置为1（0x01）。 |
| ID Length | 1字节 | NSAP地址或NET中System ID区域的长度。值为0时，表示System ID区域的长度为6字节。值为255时，表示System ID区域为空（即长度为0）。 |
| R | 1比特 | 保留比特位，设置为0。 |
| PDU Type | 5比特 | PDU的类型。
|
| Version | 1字节 | IS-IS版本号，设置为1（0x01）。 |
| Reserved | 1字节 | 保留，设置为0 (0x00)。 |
| Maximum Area Address | 1字节 | 支持的最大区域个数。设置为1～254的整数，表示该IS-IS进程实际所允许的最大区域地址数；设置为0，表示该IS-IS进程最大只支持3个区域地址数。 |
| PDU Length | 2字节 | PDU的总长度，以字节为单位。 |
| Remaining Lifetime | 2字节 | LSP的生存时间，以秒为单位。 |
| LSP ID | ID Length + 2 | 由三部分组成，System ID、伪节点ID（一字节）和LSP分片后的编号（一字节）。 |
| Sequency Number | 4字节 | LSP的序列号。 |
| Checksum | 2字节 | LSP的校验和。 |
| P | 1比特 | 自动修复（Partition Repair）位，仅与L2 LSP有关，表示路由器是否支持自动修复区域分割。 |
| ATT | 4比特 | ATT（Attachment），由Level-1-2路由器产生，用来指明始发路由器是否与其它区域相连。虽然此标志位也存在于Level-1和Level-2的LSP中，但实际上此字段只和Level-1-2路由器始发的L1 LSP有关。此字段有4bit，用来表明相连的区域所使用的度量方式。
从右至左这4位依次表示如下所示：
|
| OL | 1比特 | 过载标志OL（LSDB Overload）位。设置了过载标志位的LSP虽然还会在网络中扩散，但是在计算通过超载路由器的路由时不会被采用。即，对路由器设置过载位后，其它路由器在进行SPF计算时不会考虑这台路由器。当路由器内存不足时，系统自动在发送的LSP报文中设置过载标志位。 |
| IS Type | 2比特 | 生成LSP的路由器的类型。用来指明是Level-1还是Level-2路由器（01表示Level-1，11表示Level-2）。 |
| Variable Length Fields | 变长 |
由多个CLV（Code-Length-Value）三元组组成。CLV也称为TLV（Type-Length-Value）。不同PDU类型所包含的CLV是不同的，其中，Code值从1到10的CLV在ISO 10589中定义（有2类未在上表中列出），其他几种CLV在RFC 1195中定义。 |
三、 IS-IS LSP消息报文示例
Frame 1: 97 bytes on wire (776 bits), 97 bytes captured (776 bits)
Arrival Time: May 1, 2015 02:11:17.692716000
Epoch Time: 1430417477.692716000 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: 97 bytes (776 bits)
Capture Length: 97 bytes (776 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:llc:osi:isis]
[Coloring Rule Name: Broadcast]
[Coloring Rule String: eth[0] & 1]
IEEE 802.3 Ethernet
Destination: ISIS-all-level-1-IS's (01:80:c2:00:00:14)
Address: ISIS-all-level-1-IS's (01:80:c2:00:00:14)
.... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Source: AlcatelI_2b:c3:ba (00:20:60:2b:c3:ba)
Address: AlcatelI_2b:c3:ba (00:20:60:2b:c3:ba)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Length: 83
Logical-Link Control
DSAP: ISO Network Layer (0xfe)
IG Bit: Individual
SSAP: ISO Network Layer (0xfe)
CR Bit: Command
Control field: U, func=UI (0x03)
000. 00.. = Command: Unnumbered Information (0x00)
.... ..11 = Frame type: Unnumbered frame (0x03)
ISO 10589 ISIS InTRA Domain Routeing Information Exchange Protocol
Intra Domain Routing Protocol Discriminator: ISIS (0x83)
PDU Header Length: 27
Version (==1): 1
System ID Length: 6
PDU Type : L1 LSP (R:000)
Version2 (==1): 1
Reserved (==0): 0
Max.AREAs: (0==3): 3
ISO 10589 ISIS Link State Protocol Data Unit
PDU length: 80
Remaining lifetime: 1194
LSP-ID: 0020.602b.0006.00-00
Sequence number: 0x000283c2
Checksum: 0xcab3 [correct]
[Good Checksum: True]
[Bad Checksum: False] Type block(0x01): Partition Repair:0, Attached bits:0, Overload bit:0, IS type:1
0... .... = Partition Repair: Not supported
.000 0... = Attachment: 0
0... = Error metric: Unset
.0.. = Expense metric: Unset
..0. = Delay metric: Unset
...0 = Default metric: Unset
.... .0.. = Overload bit: Not set
.... ..01 = Type of Intermediate System: Level 1 (1)
Area address(es) (14)
Area address (13): 39.764f.8000.0000.0000.0001.0002
IS Reachability (23)
IsNotVirtual
IS Neighbor: 0020.602b.0005.00
Default Metric: 20, Internal
Delay Metric: Not supported
Expense Metric: Not supported
Error Metric: Not supported
IS Neighbor: 0020.602b.0007.00
Default Metric: 20, Internal
Delay Metric: Not supported
Expense Metric: Not supported
Error Metric: Not supported
ES Neighbor(s) (10)
ES Neighbor: 0020.602b.0006
Default Metric: 0, Internal
Delay Metric: Not supported
Expense Metric: Not supported
Error Metric: Not supported</code></pre>
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