Additional IS-IS Packet Information

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The following sections provide additional information on the following packet types:

  • IS-IS packets

  • Hello packets

  • Link-state packets

  • Sequence number packets

IS-IS Packet Fields (Alphabetical Order)

  • ATT ‚ Specifies the attachment bits (flag attachments to other areas).

  • Checksum ‚ Gives the checksum of the contents of the LSP from the source ID to the end.

  • Circuit Type ‚ Defines whether the link is Level 1 and/or Level 2.

  • End LSP ‚ Is the LSP ID of the last LSP in CSNP.

  • Holding Time ‚ Defines how long to wait for a hello from this system before clearing the adjacency .

  • ID Length ‚ Gives the length of the system ID field in an NSAP(NET).

  • Intradomain Routing Protocol Discriminator ‚ Is the network layer protocol identifier

  • IS Type ‚ Defines the type of router, Level 1 or Level 2.

  • LAN ID ‚ Consists of the system ID of the designated intermediate system, plus a unique number as an identifier of the LAN.

  • Length Indicator ‚ Gives the length of the fixed header of the packet, in bytes.

  • Local Circuit ID ‚ Is a unique identifier for a link.

  • LSP ID ‚ Is an identifier for a router's LSP, consisting of the system ID of the router, a fragment number, and a nonzero octet for the pseudonode number, in case of a pseudonode LSP.

  • Maximum Area Addresses ‚ Specifies the number of areas permitted.

  • OL ‚ Is an LSP overload bit (also represented as LSPDBOL).

  • P ‚ Is the partition repair bit.

  • PDU Length ‚ Gives the length of the packet (PDU), in bytes.

  • PDU Type ‚ Specifies the type of packet.

  • Priority ‚ Shows the priority for a node for DIS arbitration.

  • R ‚ See Reserved.

  • Remaining Lifetime ‚ Specifies the remaining time for an LSP to expire.

  • Reserved ‚ Consists of unspecified fields. Is transmitted as zeros and ignored on receipt.

  • Sequence Number ‚ Is the sequence number of the LSP.

  • Source ID ‚ Is the same as the system identifier (SysID).

  • TLV Fields ‚ Consists of Type (or code), Length, and Value fields. Also known as variable-length fields.

  • Version/Protocol ID Extension ‚ Applies to the IS-IS protocol (defined as 1).

Hello Packets

Figure 10-21. LAN Level 1 Hello Packet Format (PDU Type 15)

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Figure 10-22. LAN Level 2 Hello Packets (PDU Type 16)

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Figure 10-23. Point-to-Point Hello Packets (PDU Type 17)

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Link-State Packets

Figure 10-24. Level 1 Link-State Packets (PDU Type 18)

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Figure 10-25. Level 2 Link-State Packets (PDU Type 20)

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Sequence Number Packets

Figure 10-26. Complete Sequence Number Packets (PDU Type 24)

graphics/10fig26.gif

Figure 10-27. Level 2 Complete Sequence Number Packets (PDU Type 25)

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Figure 10-28. Level 1 Partial Sequence Number Packets (PDU Type 26)

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Figure 10-29. Level 2 Partial Sequence Number Packets (PDU Type 27)

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Troubleshooting IP Routing Protocols
Troubleshooting IP Routing Protocols (CCIE Professional Development Series)
ISBN: 1587050196
EAN: 2147483647
Year: 2002
Pages: 260

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