What indicates to a link-state router that a neighbor is unreachable?

What indicates to a link-state router that a neighbor is unreachable?

• The router no longer receives Hello packets.
• The router no longer receives routing updates.
• The router receives an LSP with previously learned information.
• The router receives an update with a hop count of 16.

Explanation: OSPF routers send Hello packets to monitor the state of a neighbor. When a router stops receiving Hello packets from a neighbor, that neighbor is considered unreachable, and the adjacency is broken.

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