What event has occurred if a router sends a notice level message to a syslog server?
When a router sends a notice level message to a syslog server, it means that an event has occurred on the router that is noteworthy and should be logged for later review.
Option B, "An interface line has changed status," is the most likely event to trigger a notice level message to be sent to a syslog server. This could happen, for example, if an interface goes down or comes back up, or if there is a change in the link speed or duplex setting on an interface. These events are important to log because they can affect the overall health and performance of the network, and may require further investigation or troubleshooting.
Option A, "A certificate has expired," is less likely to trigger a notice level message, as certificate expirations are typically logged at a lower severity level (such as informational or warning) unless they are causing more significant issues.
Option C, "A TCP connection has been torn down," and option D, "An ICMP connection has been built," are also less likely to trigger a notice level message, as these events are typically logged at a lower severity level unless they are indicative of a larger issue or security concern.
Overall, notice level messages are used to indicate important events that should be logged for later review, but are not urgent or critical in nature. The specific event that triggered the notice level message will depend on the configuration and context of the router and the network it is operating in.