JNCIS的ISIS读书笔记.docx

1、JNCIS的ISIS读书笔记第一部分 ISIS 的 PDU包头结构 11.IS-IS common PDU header12.IS-IS LAN Hello PDU23.IS-IS Point-to-Point Hello PDU34.Complete Sequence Number PDU45.Partial Sequence Number PDU56.Link-State PDU6第二部分配置选项 71.Interface Circuit ID72.Authentication73.Interface Metrics74.Mesh Groups8第三部分 TLV类型 101.Area Ad

2、dress TLV102.IS Reachability TLV103.IS Neighbors TLV114.Padding TLV125.LSP Entry TLV136.Authentication TLV137.Checksum TLV148.Extended IS Reachability TLV149.IP Internal Reachability TLV1510.Protocols Supported TLV1711.IP External Reachability TLV1712.IP Interface Address TLV1813.Traffic Engineering

3、 IP Router ID TLV1814.Extended IP Reachability TLV1915.Dynamic Host Name TLV2016.Graceful Restart TLV2017.Point-to-Point Adjacency State TLV21第一部分 ISIS的PDU包头结构1.IS-IS common PDU headerProtocol ID (1 octet)This field is set to a constant value of 0x83 and designates that the higher-level data belongs

4、 to IS-IS.Header Length (1 octet)This field indicates the total length, in octets, of the IS-IS headers. It includes both the common IS-IS header and any PDU-specific headers that follow.Version/Protocol ID Extension (1 octet)This field is set to a constant value of 0x01. The IS-IS specification def

5、ines this field as an extension area for the Protocol ID data. The JUNOS software does not implement this function.ID Length (1 octet) This field is used to inform other systems of the system ID length. For backward compatibility, the default length of 6 bytes is represented with the constant value

6、of 0x00. The JUNOS software does not use a larger ID size, so this field is set to a constant value of 0x00.PDU Type (1 octet) This field designates the PDU carried after the common header. The first 3 bits are set to 0. The remaining bit combinations include:_ Level 1 LAN Hello (15)_ Level 2 LAN He

7、llo (16)_ Point-to-Point Hello (17)_ Level 1 link-state PDU (18)_ Level 2 link-state PDU (20)_ Level 1 Complete SNP (24)_ Level 2 Complete SNP (25)_ Level 1 Partial SNP (26)_ Level 2 Partial SNP (27)Version (1 octet) This field is set to a constant value of 0x01, the current IS-IS version.Reserved (

8、1 octet) This field is set to a constant value of 0x00 and is ignored on receipt.Maximum Area Addresses (1 octet) This field is set to a constant value of 0x00. It informs other systems how many area addresses are supported by the local router. A value of 0 means that no more than three area address

9、es are assigned to this router.2.IS-IS LAN Hello PDUWe ve previously stated that IS-IS routers exchange IS-IS Hello (IIH) PDUsto establish an adjacency. While the purpose of the Hello PDU is the same, there are three different formats the router can use. One is for point-to-point links, and the two

10、others are for broadcast links one each for Level 1 and Level 2. Recall from the “ IS-IS Levels ”section earlier that L1 routers must share the same area address to form an adjacency, while L2 routers do not have this limitation. The separate LAN Hello PDUs simply tell the receiving router to check

11、or ignore this information.L1 LAN Hello PDUs are multicast to the “ AllL1 ISs ”address of 01:80:c2:00:00:14. L2 routers share aseparate multicast address “ All L2 ISs 2:”00:00:of1:80:c5.Both LAN Hello PDUs share a common packet format, as shown in Figure 7.8.The IS-IS LAN Hello PDU consists of the f

12、ollowing fields:Circuit Type (1 octet) The first 6 bits are set to 0. The remaining bits designate the level at which the interface is operating: L1 (0x01), L2 (0x02), or L1/L2 (0x03). PDUs with a value of 0x00 in this field are ignored.Source ID (6 octets) This field designates the sender of the II

13、H. The field is set to the 6-byte system ID of the sending router.Holding Time (2 octets) The value in this field represents the amount of time each neighboring router should wait before terminating the adjacency after the last received IS-IS Hello PDU from this neighbor.PDU Length (2 octets) The va

14、lue in this field represents the total length of the IS-IS Hello PDU. The field is set to a constant value of 1492 bytes (0x05D4).Priority (1 octet) The first bit is set to 0. The remainder of the byte designates the value used for the election of the DIS. The default value for the JUNOS software is

15、 64.LAN ID (7 octets) This field designates the ID of the current DIS on the broadcast circuit. The field is set to the 6-byte system ID and 1-byte circuit ID of the DIS.TLVs (Variable) This field contains information about the sending router, including the area address, neighbor ID, authentication,

16、 and interface addressing.3.IS-IS Point-to-Point Hello PDUIS-IS adjacencies on point-to-point links are also formed through the advertisement of HelloPDUs. Onbroadcast links, separate PDUs have been defined for Level 1 and Level 2. Only a singleHello PDU is defined for point-to-point links. The desi

17、re to be adjacent with a neighbor at L1, L2,or L1/L2 is encoded in the Circuit Type field within the PDU itself.Circuit Type (1 octet) The first 6 bits are set to 0. The remaining bits designate the level at which the interface is operating: L1 (0x01), L2 (0x02), or L1/L2 (0x03). PDUs with a value o

18、f 0x00 in this field are ignored.Source ID (6 octets) This field designates the sender of the IIH. It is set to the 6-byte system ID of the sending router.Holding Time (2 octets) The value in this field represents the amount of time each neighboring router should wait before terminating the adjacenc

19、y after the last received IS-IS Hello PDU.PDU Length (2 octets) The total length of the IS-IS Hello PDU is encoded in this field. The field is set to a constant value of 1492 bytes (0x05D4).Circuit ID (1 octet) This field designates the specific ID of the local router interfaces share a value of 0x0

20、1 within the JUNOS software.All point-tos-pointinterface.TLVs (Variable) This field contains information about the sending router, including the area address, authentication, and interface addressing.4.Complete Sequence Number PDUThe Complete Sequence Number PDU (CSNP) contains a complete listing of

21、 the link-statePDUs in the link-state database of the local router. The CSNP provides an identifier, a lifetime,a sequence number, and a checksum for each piece of information in the database. A CSNP issent periodically on both broadcast and point-to-point links to maintain database correctness.In a

22、ddition, CSNPs are advertised between two neighbors during the formation of an adjacency.As with the IS-IS LAN Hello PDUs, there are separate CSNPs for Level 1 and Level 2 usedon all media types.Level 1 PDUs are multicast to the “ All L1 ISs ” address of 01:80:c2:00:00:14.Level 2 PDUs are multicast

23、to the“ All L2 ISs ” address of 01:80:c2:00:00:15. Figure 7.11 showsthe format of the CSNP. The fields of the CSNP include:Length (2 octets) The total length of the CSNP, in octets, is encoded in this field.Source ID (7 octets) This field designates the sender of the CSNP. It is set to the 6-byte sy

24、stemID and 1-byte circuit ID (0x00) of the sending router.Start LSP ID (8 octets)This field is set to a constant value of 0x0000.0000.0000.00-00. Itdesignates the smallest possible LSP ID value.End LSP ID (8 octets)This field is set to a constant value of 0xFFFF.FFFF.FFFF.FF-FF. It designatesthe lar

25、gest possible LSP ID value.TLVs (Variable) This field contains the summary database information from the local router.5.Partial Sequence Number PDUAn IS-IS router uses the Partial Sequence Number PDU (PSNP)to request LSP information from a neighbor. The PSNP is also used to explicitly acknowledge th

26、e receipt of a received LSP on a point-to-point link. On a broadcast link, CSNPs are used as implicit acknowledgments.The PSNP has both a Level 1 and Level 2 variety, like the CSNP and IIH PDUs. On broadcast networks, Level1 PSNPs are multicast to the “ All L1 ISs ” address of 01:80:c2:00:00:14 and

27、Level 2 PSNPs are multicast to the “ All L2 ISs ” address of 01:80:c2:00:00:15. The format of the PSNP is shown in Figure 7.12.A Partial Sequence Number PDU includes the following fields:Length (2 octets) The total length of the PSNP, in octets, is encoded in this field.Source ID (7 octets) This fie

28、ld designates the sender of the PSNP. It is set to the 6-byte systemID and 1-byte circuit ID (0x00) of the sending router.TLVs (Variable) This field contains the requested database information or the LSP beingacknowledged.6.Link-State PDUThus far, we ve been talking about the-statelink database from

29、 numerous perspectives. IS-IS routers have formed adjacencies and compared their databases. Complete and Partial Sequence Number PDUs havebeen sent between routers to synchronize the databases. We ve failed to discuss the actual databaseinformation to this point. Let s now tackle this subject.A link

30、-state PDU (LSP)contains information about each router in the network and its connected interfaces. Metric and IS-IS neighbor information is also included. Figure 7.13 shows the format of the link-state PDU. A link-state PDU includes the following fields:Length (2 octets) The total length of the LSP

31、 is encoded in this field.Remaining Lifetime (2 octets) This field lists the amount of time, in seconds, each routershould consider the LSP active. The JUNOS software default lifetime value is 1200 seconds.LSP ID (8 octets)This field uniquely identifies the LSP throughout the network. The value isa

32、combination of the system ID (6 bytes), circuit ID (1 byte), and LSP Number value.Sequence Number (4 octets) This field is set to the current version number of the LSP. The initialnumber is 0x01 and is incremented each time the originating router updates the LSP.Checksum (2 octets) This field contains the checksum value of the PDU fields after theRemaining Lifetime. Attributes (1 octet) This field contains multiple settings rela