IS-IS LSP(Link-State Packets) Header

Appendix A. IS-IS Packet Formats

IS-IS Packet Fields (Alphabetical Order)

  • ATT— Attachment Bits (Flags attachment to other areas)
  • Checksum— Checksum of contents of LSP from source ID field to the end
  • Circuit Type— Defines whether link is Level-1 and Level-2
  • End LSP— LSP ID of last LSP in CSNP
  • Holding Time— Defines how long to wait for a hello from this system before clearing the adjacency
  • ID Length— Length of the System ID field in an NSAP(NET)
  • Intradomain Routing Protocol Discriminator— Network layer protocol identifier
  • IS Type— Defines type of router, Level-1 or Level-2
  • LAN ID— LAN Identifier, Consists of the System ID of the designated intermediate system plus a unique number
  • Length Indicator— Length of the fixed header of the packet in bytes
  • Local Circuit ID— Unique identifier for a link
  • LSP ID— Identifier for router's LSP, consisting of the System ID of the router, fragment number, and a nonzero octet for pseudonode number in case of pseudonode LSP
  • Maximum Area Addresses— Number of areas permitted
  • OL— LSP overload bit (also represented as LSPDBOL)
  • P— Partition repair bit
  • PDU Length— Length of packet (PDU) in bytes
  • PDU Type— Type of packet
  • Priority— Priority for node for DIS arbitration
  • R— See Reserved
  • Remaining Lifetime— Remaining time for an LSP to expire
  • Reserved— Unspecified fields, transmitted as 0s and ignored on receipt
  • Sequence Number— Sequence number of LSP
  • Source ID— Same as system identifier (SysID)
  • TLV Fields— Type (or code), Length and Value fields, also known as variable-length fields
  • Version/Protocol ID Extension— Of the IS-IS protocol (defined as 1)



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