Which extended ACL entry command option matches all ports less than the specified number?

The correct choice is the one that uses the "lt" command, which stands for "less than." In the context of extended Access Control Lists (ACLs) in Cisco networking, using "lt port-num" will match all traffic on ports that are numerically less than the specified port number.

For instance, if the specified port number is 80, the ACL entry would permit or deny traffic on ports 0 through 79. This functionality is critical for controlling access to resources based on port numbers, allowing network administrators to create more nuanced rules in their ACLs.

The other options do not serve this specific purpose. The "eq" command is used for an exact match, which would only apply to a single specified port. The "gt" command identifies all ports greater than the specified number, which is the opposite of what is required in this case. The "neq" command means "not equal," which allows traffic that does not match the specified port, but does not equate to matching all ports less than the specified port number. Therefore, "lt port-num" is the appropriate command for this scenario.