Four routers run IS-IS and have established adjacencies. The area IDs and router levels are marked in the following figure. R1 and R2 are connected through a PPP link, and R3 is the DIS. Which of the following statements are true?
A.
If R2 sends a Level-2 LSP, R3 needs to send a PSNP for acknowledgment.
B.
R3 periodically sends CSNPs to implement Level-2 LSDB synchronization.
C.
R2 sends an LSP to R3 and R4 in unicast mode.
D.
If R1 sends an LSP, R2 needs to send a PSNP for acknowledgment.
R3, as the DIS in the Level-2 domain, periodically sends Complete Sequence Number Protocol Data Units (CSNPs) to ensure LSDB synchronization among Level-2 routers.
R1 and R2 are in a Level-1 domain, and IS-IS requires the receiving router (R2) to acknowledge an LSP from R1 by sending a Partial Sequence Number Protocol Data Unit (PSNP).
IS-IS LSPs in a broadcast network are sent using multicast, not unicast, making option C incorrect.
For Level-2 LSPs, acknowledgments are not provided using PSNP by R3; CSNPs are sufficient for synchronization .
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