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ME60 V800R010C10SPC500 Feature Description - WAN Access 01

This is ME60 V800R010C10SPC500 Feature Description - WAN Access
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
IS-IS Control Messages

IS-IS Control Messages

IS-IS routers implement routing by exchanging control messages. This section describes IS-IS control messages.

IS-IS PDU Formats

Nine types of IS-IS protocol data units (PDUs) are available for processing control information. Each PDU is identified by a 5-digit type code. IS-IS has three major types of PDUs: Hello PDUs, Link State PDUs (LSPs), and Sequence Number PDUs (SNPs). Table 8-7 shows the mapping between PDUs and type values.

Table 8-7 Mapping between PDUs and type values

PDU Type

Acronym

Type Value

Level-1 LAN IS-IS Hello PDU

L1 LAN IIH

15

Level-2 LAN IS-IS Hello PDU

L2 LAN IIH

16

Point-to-Point IS-IS Hello PDU

P2P IIH

17

Level-1 Link State PDU

L1 LSP

18

Level-2 Link State PDU

L2 LSP

20

Level-1 Complete Sequence Numbers PDU

L1 CSNP

24

Level-2 Complete Sequence Numbers PDU

L2 CSNP

25

Level-1 Partial Sequence Numbers PDU

L1 PSNP

26

Level-2 Partial Sequence Numbers PDU

L2 PSNP

27

The first eight bytes in all IS-IS PDUs are public. Figure 8-33 shows the IS-IS PDU format.
Figure 8-33 IS-IS PDU format
The main fields are as follows:
  • Intradomain Routing Protocol Discriminator: network layer protocol identifier assigned to IS-IS, which is 0x83.
  • Length Indicator: length of the fixed header, in bytes.
  • ID Length: length of the system ID of network service access point (NSAP) addresses or NETs in this routing domain.
  • PDU Type: type of a PDU. For details, see Table 8-7.
  • Maximum Area Address: maximum number of area addresses supported by an IS-IS area. The value 0 indicates that a maximum of three area addresses are supported by this IS-IS area.
  • Type/Length/Value (TLV): encoding type that features high efficiency and expansibility. Each type of PDU contains a different TLV. Table 8-8 shows the mapping between TLV codes and PDU types.
    Table 8-8 Mapping between TLV codes and PDU types

    TLV Code

    TLV Code Name

    PDU Type

    1

    Area Addresses

    IIH, LSP

    2

    IS Neighbors (LSP)

    LSP

    4

    Partition Designated Level2 IS

    L2 LSP

    6

    IS Neighbors (MAC Address)

    LAN IIH

    7

    IS Neighbors (SNPA Address)

    LAN IIH

    8

    Padding

    IIH

    9

    LSP Entries

    SNP

    10

    Authentication Information

    IIH, LSP, or SNP

    128

    IP Internal Reachability Information

    LSP

    129

    Protocols Supported

    IIH or LSP

    130

    IP External Reachability Information

    L2 LSP

    131

    Inter-Domain Routing Protocol Information

    L2 LSP

    132

    IP Interface Address

    IIH or LSP

Hello Packet Format

Hello packets, also called the IS-to-IS Hello PDUs (IIHs), are used to set up and maintain neighbor relationships. Level-1 LAN IIHs are applied to the Level-1 routers on broadcast LANs. Level-2 LAN IIHs are applied to the Level-2 routers on broadcast LANs. P2P IIHs are applied to non-broadcast networks. IIHs in different networks have different formats.
  • LAN IIHs: Figure 8-34 shows the format of IIHs on a broadcast network.
    Figure 8-34 Level-1/Level-2 LAN IIH format

  • P2P IIHs: Figure 8-35 shows the format of IIHs on a P2P network.
    Figure 8-35 P2P IIH format

    As shown in Figure 8-35, most fields in a P2P IIH are the same as those in a LAN IIH. The P2P IIH does not have the priority and LAN ID fields but has a local circuit ID field. The local circuit ID indicates the local link ID.

LSP Format

LSPs are used to exchange link-state information. There are two types of LSPs: Level-1 and Level-2. Level-1 IS-IS transmits Level-1 LSPs. Level-2 IS-IS transmits Level-2 LSPs. Level-1-2 IS-IS can transmit both Level-1 and Level-2 LSPs.

Level-1 and Level-2 LSPs have the same format, as shown in Figure 8-36.

Figure 8-36 Level-1 or Level-2 LSP

The main fields are as follows:

  • ATT: Attached bit

    ATT is generated by a Level-1-2 router to identify whether the originating router is connected to other areas. When a Level-1 router receives a Level-1 LSP with ATT as 1 from a Level-1-2 router, the Level-1 router generates a default route destined for the Level-1-2 router so that data can be transmitted to other areas.

    Although ATT is defined in both the Level-1 LSP and Level-2 LSP, it is set only in the Level-1 LSP only by the Level-1-2 router.

  • OL: LSDB overload

    LSPs with the overload bit are still flooded on networks, but the LSPs are not used when routes that pass through a device configured with the overload bit are calculated. That is, after a device is configured with the overload bit, other devices ignore the device when performing the SPF calculation except for the direct routes of the device.

  • IS Type: type of the IS-IS generating the LSP

    IS Type is used to specify whether the IS-IS type is Level-1 or Level-2 IS-IS. The value 01 indicates Level-1; the value 11 indicates Level-2.

SNP Format

SNPs describe the LSPs in all or some of the databases and are used to synchronize and maintain all LSDBs. SNPs consist of complete SNPs (CSNPs) and partial SNPs (PSNPs).
  • CSNPs carry summaries of all LSPs in LSDBs, which ensures LSDB synchronization between neighboring routers. On a broadcast network, the designated intermediate system (DIS) sends CSNPs at an interval. The default interval is 10 seconds. On a P2P link, neighboring devices send CSNPs only when a neighbor relationship is established for the first time.

    Figure 8-37 shows the CSNP format.

    Figure 8-37 Level-1/Level-2 CSNP format

    The main fields are as follows:

    • Source ID: system ID of the router that sends SNPs

    • Start LSP ID: ID of the first LSP in a CSNP

    • End LSP ID: ID of the last LSP in a CSNP

  • PSNPs list only the sequence numbers of recently received LSPs. A PSNP can acknowledge multiple LSPs at a time. If an LSDB is not updated, PSNPs are also used to request a new LSP from a neighbor.

    Figure 8-38 shows the PSNP format.

    Figure 8-38 Level-1/Level-2 PSNP format

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Updated: 2019-01-04

Document ID: EDOC1100059473

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