Explanation:
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Explanation of IS-IS Packet Types and Synchronization Process:
In the given scenario, R2 requests LSPs from R1 to synchronize its Link State Database (LSDB). The following IS-IS packet types are involved in this synchronization process:
1. P2P IIH (Point-to-Point IS-IS Hello):
* Purpose: Establishes and maintains IS-IS neighbor relationships.
* Step: This packet is exchanged initially to detect and maintain the adjacency between R1 and R2.
2. PSNP (Partial Sequence Number PDU):
* Purpose: Requests missing or outdated LSPs (Link State PDUs) from a neighbor to synchronize the LSDB.
* Step: In this case, R2 sends a PSNP to R1 to request the missing or outdated LSP.
3. LSP (Link State PDU):
* Purpose: Contains routing information and is used to update the LSDB.
* Step: R1 sends the requested LSPs to R2 for synchronization.
4. CSNP (Complete Sequence Number PDU):
* Purpose: Lists all LSPs in the sender's LSDB to help neighbors verify and request missing LSPs.
* Step: R1 sends a CSNP during retransmission timeout to notify R2 of its LSPs.