Exam Code 642-801 (BSCI)

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Q9. Match the following in the context of an OSPF area:
                1. LSU    A. This packet is sent by slave router if the DDP has more up-to-date link-state entry.
                2. LSA    B. This packet is sent when a router notices a change in a link-state
                3. LSR    C. These are contained in LSPs and have the information about neighbors and path costs.

                        A. 1->A; 2->B; 3->C

                        B. 1->B; 2->A; 3->C

                        C. 1->B; 2->C; 3->A

                         D. 1->C; 2->A; 3->B

Ans: C

Explanation:  

1. LSA (Link State Advertisement): LSAs are included in the database description packets (DDPs or DBDs). LSA entries include link-state type, the address of the advertising router, the cost of the link, and the sequence number.
2. LSR ( Link State Request): When a slave router receives an DDP (Database Description Packet), it sends and LSAck packet. Then it compares the received information with the information it has. If the DDP has more recent information, the slave router sends a link-state request (LSR) to the master router.
3. LSU ( Link State Update): LSU packet is sent in response to LSR (Link-State Request) packet sent from a slave router to a master router. LSU contains complete information about the requested entry.

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