The following sections provide additional information on the following packet types:
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ATT ‚ Specifies the attachment bits (flag attachments to other areas).
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Checksum ‚ Gives the checksum of the contents of the LSP from the source ID to the end.
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Circuit Type ‚ Defines whether the link is Level 1 and/or Level 2.
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End LSP ‚ Is the LSP ID of the last LSP in CSNP.
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Holding Time ‚ Defines how long to wait for a hello from this system before clearing the adjacency .
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ID Length ‚ Gives the length of the system ID field in an NSAP(NET).
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Intradomain Routing Protocol Discriminator ‚ Is the network layer protocol identifier
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IS Type ‚ Defines the type of router, Level 1 or Level 2.
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LAN ID ‚ Consists of the system ID of the designated intermediate system, plus a unique number as an identifier of the LAN.
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Length Indicator ‚ Gives the length of the fixed header of the packet, in bytes.
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Local Circuit ID ‚ Is a unique identifier for a link.
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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.
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Maximum Area Addresses ‚ Specifies the number of areas permitted.
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OL ‚ Is an LSP overload bit (also represented as LSPDBOL).
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P ‚ Is the partition repair bit.
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PDU Length ‚ Gives the length of the packet (PDU), in bytes.
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PDU Type ‚ Specifies the type of packet.
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Priority ‚ Shows the priority for a node for DIS arbitration.
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R ‚ See Reserved.
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Remaining Lifetime ‚ Specifies the remaining time for an LSP to expire.
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Reserved ‚ Consists of unspecified fields. Is transmitted as zeros and ignored on receipt.
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Sequence Number ‚ Is the sequence number of the LSP.
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Source ID ‚ Is the same as the system identifier (SysID).
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TLV Fields ‚ Consists of Type (or code), Length, and Value fields. Also known as variable-length fields.
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Version/Protocol ID Extension ‚ Applies to the IS-IS protocol (defined as 1).