Both firewalls and proxy servers allow you to protect an internal Intranet from unauthorized access over the Internet. Firewalls typically use a packet-filtering mechanism, and are configured using sets of rules that define the actions to be taken on network traffic based on protocol and port properties. Citrix ICA traffic uses the registered port 1494 with the TCP protocol. Allowing ICA traffic through a firewall generally entails defining a rule to allow port access for port 1494 traffic in the proper direction.
Proxy servers represent another type of network security, based on an application-level gateway.
Traffic is relayed between networks by an application based on rule sets similar to the firewalls mentioned above. However, proxy servers are generally not as configurable since they rely on application code to perform traffic filtering. Citrix is currently investigating approaches for supporting proxy servers, but no proxy server support is available at this time.