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)