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Proxy

Proxy servers can add the following HTTP headers.

Response headers

Forwarded

The newer, standardized form for X-Forwarded-For, X-Forwarded-Host, X-Forwarded-Protocol. (IPv6 addreses should be encapsulated in square brackets.)

Forwarded: by=<identifier>;for=<identifier>;host=<host>;proto=<http|https>, ...
Forwarded: for=192.0.2.60;proto=http;by=203.0.113.43
Forwarded: for=192.0.2.43, for="[2001:db8:cafe::17]"

X-Forwarded-For

Identifies the originating IP address of a client passing through HTTP proxies and/or load balancers.

X-Forwarded-For: <client>, <proxy1>, <proxy2>, ...
X-Forwarded-For: 203.0.113.195, 70.41.3.18, 150.172.238.178

X-Forwarded-Host

Identifies the original host requested by the client (in the initial Host request header).

X-Forwarded-Host: <host>
X-Forwarded-Host: lalala.example-cdn.com

X-Forwarded-Protocol

Identifies the original protocol used by the client to connect to your proxy or load balancer.

X-Forwarded-Proto: https

Other headers

Via

Added by proxies, can appear in response/request headers.

Used for "tracking message forwards, avoiding request loops, and identifying the protocol capabilities of senders along the request/response chain" (MDN)

  • <protocol-name> — the name of the protocol used, e.g. HTTP
  • <protocol-version> — version of the protocol, e.g. 1.1
  • <host> or <host>:<port> — public proxy URL
  • <pseudonym> — name/alias of an internal proxy
Via: [ <protocol-name> "/" ] <protocol-version> <host> [ ":" <port> ]
Via: [ <protocol-name> "/" ] <protocol-version> <pseudonym>
Via: HTTP/1.1 GWA
Via: HTTP/1.0 fred, HTTP/1.1 p.example.net

References