pfSense

If you have a host alias using a numerical name such as "2222", then using port "2222" (literal) in firewall rules is prevented by the GUI due to an input validation error:

The following input errors were detected:

    2222 is not a valid start destination port. It must be a port alias or integer between 1 and 65535.
    2222 is not a valid end destination port. It must be a port alias or integer between 1 and 65535.

Due to the fact that an alias exists called "2222", the field is interpreted as the alias name rather than the literal port number even though the second case is valid.