What are three circumstances under which a router sends link-state PDUs (LSPs)?
(Choose three)
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A. B. C. D. E.BCE
Link-state PDUs (LSPs) are used by routers in a link-state routing protocol to exchange information about the state of the network. Here are the three circumstances under which a router sends LSPs:
When there is a network change: Whenever there is a change in the network topology, such as the addition or removal of a router, or a change in the link state of a router, the router sends an LSP to its neighbors. This allows the neighbors to update their own routing tables to reflect the change in the network topology.
During adjacency formation: Adjacency formation is the process by which two neighboring routers establish a communication link. During this process, each router sends an LSP to the other to exchange information about the state of the network. This allows the routers to synchronize their routing tables and ensure that they have the same information about the network.
Periodically every 9 seconds: In most link-state routing protocols, routers send LSPs periodically, even if there have been no changes in the network topology. This helps to ensure that all routers have the most up-to-date information about the state of the network. The frequency at which LSPs are sent can vary depending on the specific routing protocol and network configuration.
The following options are incorrect:
D. LSPs are sent in response to CSNP messages: CSNP (Complete Sequence Number Packet) messages are used in OSPF (Open Shortest Path First) to synchronize the LSDB (Link State Database) between routers. LSPs are not sent in response to CSNP messages.
E. LSPs are sent in response to PSNP messages: PSNP (Partial Sequence Number Packet) messages are used in OSPF to request missing LSPs from neighboring routers. LSPs are not sent in response to PSNP messages.
In summary, routers send LSPs when there is a network change, during adjacency formation, and periodically to ensure that all routers have the most up-to-date information about the state of the network.