IS-IS Packet Types for Database Synchronization

CD

The Intermediate System to Intermediate System (IS-IS) protocol is a link-state routing protocol that operates at the OSI layer 2 level. IS-IS uses different types of packets to perform its functions, including maintaining the database synchronization. The following are the IS-IS packet types that are used for database synchronization:

A. IIH (IS-IS Hello) packets: These packets are used for neighbor discovery, adjacency formation, and maintenance. IIH packets are sent out regularly to all the neighbors to maintain the link-state database. When a new adjacency is formed, the two routers exchange IIH packets to exchange information about the router ID, system ID, and other parameters.

B. LSP (Link-State Protocol) packets: These packets are used to flood the network with information about the topology of the network. The LSPs are generated by each router and contain information about the router itself, its directly connected neighbors, and the links between them. The LSPs are flooded throughout the network, allowing each router to build a complete view of the network topology.

C. PSNP (Partial Sequence Number PDU) packets: These packets are used to request missing LSPs from a neighbor. A router sends a PSNP packet to its neighbor when it detects that it is missing an LSP. The PSNP packet contains a list of missing LSPs, and the neighbor sends the missing LSPs back in response.

D. CSNP (Complete Sequence Number PDU) packets: These packets are used to synchronize the entire link-state database between routers. The CSNP packets are sent periodically by each router and contain a list of all the LSPs in the database. The receiving router compares the list to its own database and requests any missing LSPs using PSNP packets.

Therefore, the correct answers are A (IIH) and D (CSNP) packets are used to maintain the IS-IS database synchronization.