A monitor has been defined with an alias port of 443. All other options are left at their defaults. The administrator wishes to assign it to a pool of members where the members' ports vary. Which is t

A member is not automatically marked down because its configured port differs from the monitor's alias port - the alias port redirects the probe destination, it does not enforce a port-match requirement for member status.

The alias port on a BIG-IP monitor overrides the member's service port strictly for health check probe purposes, so the monitor will contact every node at port 443 regardless of what port the pool member is configured to serve on. This allows administrators to verify a specific service (such as HTTPS) on the underlying node IP while traffic is directed to a different member port. Members are marked up or down based solely on the health check result at port 443 on their node address.

The monitor does not conditionally attempt SSL checks based on whether the member's service port happens to be an SSL port - the alias port of 443 is used unconditionally for every probe regardless of member port.

BIG-IP explicitly allows assigning a monitor with an alias port to pools whose members use different service ports - the alias port feature is designed to provide this kind of decoupled monitoring flexibility.