Gateways and Proxy Gateways

NCSA Mosaic for Microsoft Windows User's Guide

Gateways and Proxy Gateways

For a variety of reasons, NCSA Mosaic is sometimes unable to access documents directly. Under such circumstances, NCSA Mosaic use can gateways to access and retrieve the desired files. The two most common circumstances that require the use of gateways are as follows:

The files being accessed are in a format or on a type of server that NCSA Mosaic does not handle directly.
WAIS gateways, for example, can provide multi-document search capabilities. Other gateways find information for a client, convert it to HTML format, and send the formatted document back to the client.
NCSA Mosaic is running on a system behind a protective firewall, a device some organizations employ to protect their subnet(s) and systems from uninvited intruders and from the dangers of unexamined imported files (e.g., viruses).
In such circumstances, NCSA Mosaic clients can often access the Internet only through a proxy gateway, which can be thought of as straddling the firewall (see below).

Gateways generally perform the following functions:

Receive an information request from a client.
Seek out and retrieve the requested information.
Return the requested document to the original client or generate a document on the fly to fulfill the client request.

Proxy Gateways (Proxy Servers)

Firewalls are employed by many agencies and companies to protect their systems from unwanted intrusion or contamination. Unfortunately, firewalls also make it more difficult for an NCSA Mosaic client to access a retrieve files from the Internet, beyond the firewall.

A proxy gateway allows an NCSA Mosaic client on a protected system to request information from outside the firewall. The proxy gateway, or proxy server, can be thought of as securely straddling the firewall. The proxy gateway receives the Internet request from the protected client (generally as a URL), retrieves the requested information, and returns the requested document to the client.

Proxy gateways may also exercise discretion, deciding which requests to honor and which to turn down. The criteria for such decisions will vary by installation, but may include server type, known or unknown URLs or machine addresses, or the requesting client's user ID.

Except in the screening of Internet requests, a well-implemented proxy gateway is usually transparent to the user. Your mosaic.ini file will contain a [Proxy Information] section if it is configured to use a proxy gateway.

National Center for Supercomputing Applications / mosaic-win@ncsa.uiuc.edu