Proxy Headers: X-Forwarded-For, Via, and Anonymity

What Are Proxy Headers?

When an HTTP proxy forwards your request to a destination server, it may add or modify certain headers that reveal the proxy's presence — or even your real IP address. Understanding these headers is critical for maintaining anonymity.

X-Forwarded-For (XFF)

The X-Forwarded-For header is the most common way proxies identify the originating client IP. Each proxy in the chain appends the previous hop's IP address:

X-Forwarded-For: 203.0.113.50, 198.51.100.10

In this example, 203.0.113.50 is the original client and 198.51.100.10 is the first proxy. Destination servers can read this header to discover your real IP, even behind a proxy.

Via Header

The Via header identifies the proxy software and protocol version used in the request chain:

Via: 1.1 proxy.example.com (Squid/5.7)

This tells the server that a Squid proxy handled the request, immediately flagging the connection as proxied.

Proxy Anonymity Levels

Proxies are classified by how they handle these headers:

• Transparent — forwards your real IP in X-Forwarded-For. Offers no anonymity.
• Anonymous — identifies itself as a proxy (via Via) but hides your IP.
• Elite/High-anonymous — strips all proxy-related headers. The server cannot detect proxy usage.

Header Stripping

Elite proxies remove X-Forwarded-For, Via, X-Proxy-ID, and similar headers before forwarding requests. This makes them indistinguishable from direct connections.

Testing Your Proxy Headers

Use our Proxy Checker to verify what headers your proxy sends. For protocol-level differences, see HTTP vs SOCKS5 proxies. Note that SOCKS proxies do not add HTTP headers, as they operate at a lower network layer.