A proxy server is a variation of an application-level firewall or circuit-level firewall.
It is a server application that acts as an intermediary between a client requesting a resource and the server providing that resource.
Possible proxy features:
- NAT
- Caching
- Content Filtering
Proxy Server Types
- by direction
- by transparency
Proxy Server Type by Direction
Proxy servers can be either a forward proxy or reverse proxy.
A forward proxy is an Internet-facing proxy used to retrieve data from a wide range of sources (in most cases, anywhere on the Internet). It centralizes calls from internal clients towards external server (i.e., the internet), and manage their replies.
A reverse proxy is usually an internal-facing proxy used as a front-end to control and protect access to a server on a private network. It centralizes calls from multiple clients towards a bunch of internal servers, and address the calls to the corresponding server and its reply.
Proxy Server Type by Transparency
A transparent proxy is the one that does not requires that clients are not configured to send queries directly to proxy by t the network routes outbound traffic to a proxy anyway.
A nontransparent proxy is in use hen a client is configured to send outbound queries directly to a proxy.
The settings for a nontransparent proxy can be set manually or using a proxy auto-config (PAC) file. PAC can be implemented with a script or via DHCP.