A proxy server sits between a client and the destination and makes requests on the client's behalf. The destination sees the proxy's address, and the proxy can cache, filter, log or modify traffic.
Why it matters
Forward proxies serve users, for example in a company that filters web access or a scraper that rotates addresses. Reverse proxies serve websites, handling TLS, caching and load distribution. Proxies often add headers such as X-Forwarded-For so the real client address is not lost, but applications must trust those headers only from known proxies.
Example
$ curl -x http://proxy.example.net:3128 https://example.com -I
HTTP/2 200The request goes to the proxy on port 3128, which fetches example.com and relays the response. The site logs the proxy's IP, not yours.
Common mistakes
- Trusting X-Forwarded-For from any client, which lets anyone spoof their IP.
- Expecting an HTTP proxy to protect non-web traffic.
- Using free public proxies that can read and alter unencrypted traffic.
Related
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