Connecting through a Socks proxy server

Many organizations use Socks proxy servers to protect computing resources behind a firewall. Socks is a protocol for TCP/IP-based network proxies. It allows applications on one side of a Socks proxy server to gain full access to hosts on the other side of the Socks proxy server without directly connecting to them. Proxy servers are generally used in conjunction with firewalls. Under the Socks protocol, a client that requests a connection to a host system through a firewall actually connects to a Socks proxy server. The Socks proxy server acts as an intermediary between the client and the host system. It authorizes communication requests, connects to the host on behalf of the client, and relays data between the two systems.

Z and I Emulator for Web supports both version 4 and version 5 of the Socks protocol.

• Socks version 4 specifies the message format and conventions to allow TCP-based application users access across a firewall. It provides access control based on TCP header information, including IP addresses and source and destination port numbers.
• Socks version 5 (also known as authenticated firewall traversal (AFT)) is an open Internet standard for network proxies. It adds authentication, better support for resolving domain names, support for IPv6 addresses, and other features to version 4. These features are very useful for clients located outside a firewall. A Socks user ID and password for the proxy server can optionally be sent over the connection between the Z and I Emulator for Web client and the proxy server. The user ID and password are not encrypted. For more information on version 5, see Socks Protocol Version 5.

The Java Virtual Machine (JVM) used in most Web browsers supports Socks version 4. A session can access either a Socks version 4 or version 5 proxy server, bypassing the proxy server settings in the Web browser. You can also have the session negotiate a Socks version 4 connection if the proxy server does not support version 5. For more information on Socks proxy server settings, refer to Proxy Server.