On an IS-IS network, routers send LSPs to exchange link state information. LSPs are classified into Level-1 LSPs and Level-2 LSPs and have the same format.
Which of the following parts constitute the LSP ID in an LSP?
- LSP Number
- Pseudonode ID
- System ID
- IS Type
Answer(s): A,B,C
Explanation:
IS-IS Overview: Intermediate System to Intermediate System (IS-IS) is a link-state routing protocol. Routers exchange Link State Packets (LSPs) to maintain a synchronized link-state database. These LSPs are categorized into Level-1 LSPs (intra-area routing) and Level-2 LSPs (inter-area routing). Both types share the same packet format.
Reference:
HCIP-Datacom-Core Technology Training Material (IS-IS LSPs and Packet Structure).
LSP ID Format: The LSP ID uniquely identifies each LSP and ensures accurate routing information. It comprises the following components:
System ID (C): A 6-byte identifier assigned to each router, derived from the router's NET (Network Entity Title). This identifier ensures unique identification of routers within the IS-IS domain.
Pseudonode ID (B): Assigned when a router acts as a Designated Intermediate System (DIS) on a broadcast network. It differentiates LSPs generated by the DIS from other routers.
LSP Number (A): A 1-byte field indicating the sequence number of the LSP. It helps distinguish multiple LSPs generated by the same router for the same level.
HCIP-Datacom Advanced Routing & Switching Technology (IS-IS LSP Format).
IS Type Exclusion:
IS Type (D) is not part of the LSP ID itself. It is a field within the IS-IS PDU that indicates the type of Intermediate System (Level-1, Level-2, or both) but does not contribute to the composition of the LSP ID.
HCIE-Datacom V1.0 Training Material (IS-IS Basics and Levels).
Conclusion: The LSP ID in IS-IS consists of System ID, Pseudonode ID, and LSP Number. These components uniquely identify each LSP within the IS-IS domain.