What is contained in an IS-IS CSNP message?
A.
all of the headers of the LSPs in a router’s link-state database
B.
all of the IP routes in a router’s link-state database
C.
all of the IP routes in a router’s routing table
D.
all of the LSPs in a router’s link-state database
ANswer is D
Complete Sequence Number PDU
The complete sequence number PDU (CSNP) lists all the link-state PDUs (LSPs) in the link-state database of the local router. Contained within the CSNP is an LSP identifier, a lifetime, a sequence number, and a checksum for each entry in the database. Periodically, a CSNP is sent on both broadcast and point-to-point links to maintain a correct database. Also, the advertisement of CSNPs occurs when an adjacency is formed with another router. Like IS-IS hello PDUs, CSNPs come in two types: Level 1 and Level 2.
When a device receives a CSNP, it checks the database entries again its own local link-state database. If it detects missing information, the device requests specific LSP details using a partial sequence number PDU (PSNP).