Accessing the Internet through a firewall

Mac OS X 10.4 - Accessing the Internet through a firewall

If your computer is connected to a local network that is protected from the
Internet by a firewall, you may need to specify proxy servers or use the FTP
passive mode (PASV) to access some Internet sites. A proxy server is a
computer on a local network that acts as an intermediary between a single
computer user and the Internet, so that the network can ensure security,
administrative control, and caching service.

To specify proxy servers:

1. Open System Preferences and click Network.
2. Choose a location from the Location pop-up menu if you have
set one up.
3. Choose the configuration you want to use from the Show popup
menu, such as Internal or External Modem. Then click
4. Select a proxy server, such as FTP Proxy, and then type its
address and port number in the fields on the right. If the proxy
server is protected by a password, enter your account name and
password in the dialog that appears.

If you're not sure which proxy servers to use, or if you need a password to
access the server, ask your network administrator.
You can also choose to bypass proxy settings for specific computers on the
Internet (hosts) and segments of the Internet (domains) by adding the
address of the host or domain in the field. This might be useful if you want to
make sure you are receiving information directly from the host or domain, and
not information that is cached on the proxy server.