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When looking at it in this simple manner, proxies really exists in many different
products. For example, most portal technologies that are readily available today
request content on behalf of the user and assemble the content into a single
“portal view.” The Notes “passthru” that has existed in Lotus Notes for a number
of years and that allowed remote access into Notes environments during the
early Internet years is another example of a proxy. Nevertheless, we will focus on
standalone proxy products for the rest of this section because the most generally
accepted best practice today is to use standalone proxy services.
5.3 Types of proxies
5.3.1 Forward proxies
This section defines the various types of proxies that exist in the marketplace,
and in the average infrastructure. As stated earlier, it is common that a given
proxy product will actually implement or support multiple types of proxy services.
For example, a proxy server may provide caching and authentication capabilities
in addition to the basic application proxying. However, we will treat these key
capabilities of proxies as separate proxy types to simplify this discussion.
The key proxy types that we define and discuss in this section are:
► Forward proxies
► Transparent proxies
► Caching proxies
► Security proxies
► Reverse proxies
A forward proxy is a proxy that serves users from one security zone by fulfilling
requests for content from the “next” zone, following a direction that is typically,
but not necessarily, outbound (that is, the client is inside and the server is
somewhere in the open Internet).
From a security point of view, a simple proxy has the security goal of hiding the
identity (in internal network topology terms) of the requester user workstation or
process. It can also be used to mask out some other attributes of the user
session.
A typical example of the type is the corporate proxies that serve internal users,
allowing them to access external sites for Web browsing or any other kind of
Internet connectivity.
Chapter 5. Proxies 167