[spumer]

For connect you should use only server port.
Proxy port it's internal and only for caching logic purposes.

For example:
27015 - server/game port
27915 - proxy port (where caching service is running and waiting queries)

How it works?
Kernel module will redirect INFO queries sended to 27015 port to 27915. And redirect answer back (27915 -> 27015), transparently.
Other game traffic will be passed as is.

In that case you and anyone should connect only to 27015 (server/game port). Always.