# What is a Proxy Server?

> A proxy server is an intermediary that receives a client’s request and makes a corresponding request toward another server.

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## Content

In the usual forward-proxy role, clients or their network select the proxy, which represents them to destination services. A proxy can terminate, relay, tunnel, cache, filter, or transform traffic, depending on the protocol and configuration.

Organizations use forward proxies to govern outbound web access, authenticate users, restrict destinations, cache content, or record security events. For HTTPS, a proxy may relay an opaque tunnel using HTTP CONNECT or, with separately managed trust, terminate and inspect TLS. Those modes have very different privacy, compatibility, and security consequences.

### Key points

- **Traffic steering:** Clients may be configured explicitly, discover a proxy, use an endpoint agent, or have traffic redirected by the network. Bypass routes and unsupported protocols must be considered.
- **Trust boundaries:** Validate destination names and certificates, restrict relay destinations and ports, protect administrative interfaces, and do not trust forwarded identity or address headers without a defined trusted path.
- **Privacy and records:** Proxy logs and inspected content can contain credentials, health information, searches, and other personal data. Limit collection, access, retention, and geographic transfer to a documented purpose.
- **Important limitation:** A proxy is not inherently a firewall, anonymity service, malware detector, or encryption control. Tunneling may hide content from it; inspection can weaken end-to-end confidentiality; direct paths can bypass it. Its compromise may expose both traffic and stored credentials or logs.

### Related terms

[Reverse proxy](<https://yellowcube.eu/glossary/reverse-proxy/>) · [Transparent proxy](<https://yellowcube.eu/glossary/transparent-proxy/>) · [Open proxy](<https://yellowcube.eu/glossary/open-proxy/>) · [Secure web gateway (SWG)](<https://yellowcube.eu/glossary/secure-web-gateway/>) · [Firewall](<https://yellowcube.eu/glossary/firewall/>) · [Proxy firewall](<https://yellowcube.eu/glossary/proxy-firewall/>)

### Sources

[RFC 9110: HTTP Semantics](https://www.rfc-editor.org/rfc/rfc9110) · [NIST CSRC glossary: Proxy](https://csrc.nist.gov/glossary/term/proxy)

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