What Is a Proxy Server? Forward vs Reverse

TL;DR

• A proxy server is an intermediary that passes requests and answers between a client and a destination server [1].
• A forward proxy acts for the users and can hide their addresses. A reverse proxy acts for the website and protects its servers: forward hides the client, reverse hides the server [1].
• A proxy is not the same as a VPN. A VPN usually encrypts all of a device's traffic, while a proxy typically handles particular apps and may not encrypt anything.
• You are trusting whoever runs the proxy with your traffic.

Forward proxies and reverse proxies #

A proxy sits in the middle of a connection. Instead of two computers talking directly, each talks to the proxy, which relays the messages [1]. Think of a receptionist: callers talk to the front desk, which passes messages on.

Forward proxy (acts on behalf of clients). Your request goes to the proxy, which fetches the page for you. The website sees the proxy's address instead of yours [1]. Organisations use these to filter content, monitor use and cache popular pages to save bandwidth [1][2].

Reverse proxy (acts on behalf of servers). It sits in front of a website's servers. Visitors connect to it, and it passes requests to the right server behind the scenes. Typical jobs are load balancing across several servers, caching images and files, compressing content, and protecting or hiding the real servers [1][2].

Some proxies are set up without you knowing. A transparent proxy is placed in the network path so devices need no settings, and businesses and some internet providers use it to enforce rules or cache content [2].

Because a proxy replaces the real sender's address, websites behind a reverse proxy lose sight of the visitor's address. Headers such as Forwarded and X-Forwarded-For pass the original address along. These can be faked by a client, so a site should only trust the parts added by its own proxies [1][3].

How a proxy differs from a VPN #

A forward proxy and a VPN can both make a website see a different address, which is why they get confused. The usual differences:

• Scope. A proxy is often set for one browser or app. A VPN normally covers the whole device.
• Encryption. A VPN encrypts traffic between you and its server. A basic proxy may not add any encryption of its own, though traffic to HTTPS sites stays encrypted end to end [1].
• Who sees what. In both cases the operator can see your traffic, unless it is encrypted.

See the VPN guide for more on what a VPN does and does not hide.

Risks to know about #

• Traffic exposure. A proxy operator can capture data passing through it, including passwords and cookies, unless the connection is encrypted [2].
• Open proxies. Proxies anyone can use are often run by unknown people, so treat free ones with caution [2].
• Blocking. Sites may block known proxy addresses [2].
• Misconfiguration. A badly configured proxy can expose a network that was supposed to be private [2].

FAQ #

Is a proxy server the same as a VPN? #

No. Both can show a different address to websites, but a VPN generally tunnels and encrypts all device traffic, while a proxy usually handles specific apps and may not encrypt anything.

Does a proxy make me anonymous? #

Not fully. It hides your address from the site, but the proxy operator can see your requests, and logins and cookies still identify you [2].

What is a reverse proxy used for? #

Websites use one to share traffic across servers, speed up pages with caching, and keep their real servers out of direct view [1].

Is it legal to use a proxy? #

Proxies are widely used by schools and companies and are legal in most places, but rules differ by country and by service, so check local rules and terms of use.

Sources #