By default, Microsoft Forefront Threat Management Gateway listens on port 80 for Hypertext Transfer Protocol (HTTP) requests. If, however, connecting clients are expected to use a different port, you should change the port number accordingly. You can also enable the Web listener to listen for Secure Sockets Layer (SSL) requests, on the default port 443. If you choose SSL, an appropriate certificate must first be installed on the Forefront TMG computer. You must select a server certificate to be used by the Web listener so that the Forefront TMG computer can authenticate itself to the client.