Which statement is true about IS-IS PDUs?

A.
CSNPs are exchanged only during initial adjacency establishment when a complete LSDB is
being built.

B.
PSNPs contain header information for all link-state PDUs in the IS-IS database.

C.
Both the DIS and the backup DIS broadcast CSNPs over a broadcast link.

D.
Separate CSNP and PSNP types exist for Level 1 and Level 2 systems.