What does HTTP status 306 (Switch Proxy) mean?

 
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HTTP_STATUS_USE_PROXY HTTP_STATUS_TEMPORARY_REDIRECT

HTTP_STATUS_SWITCH_PROXY

This code had an early historical meaning but is no longer defined for normal HTTP use. A server returning 306 is therefore using a vendor-specific or obsolete behavior.

Do not implement generic client handling for it. Preserve the response headers and body, then identify the server, proxy, or test tool that emitted it.

IANA HTTP Status Code Registry

Operational meaning of HTTP 306 for HTTP_STATUS_SWITCH_PROXY

HTTP 306 (HTTP_STATUS_SWITCH_PROXY) is a redirection response. AllStat records its meaning as “306 Switch Proxy”. For HTTP_STATUS_SWITCH_PROXY, interpret it with the request method, selected representation, response headers, and the specification or product that defines the code; the number alone does not prove that application work completed.

Client and server handling for HTTP_STATUS_SWITCH_PROXY

  • Apply the method-rewrite and caching rules defined for HTTP_STATUS_SWITCH_PROXY, not a generic redirect rule.
  • For HTTP_STATUS_SWITCH_PROXY, validate the Location target and prevent redirect loops across proxies or canonicalization layers.
  • For HTTP_STATUS_SWITCH_PROXY, log the original URL, target URL, method, and cache decision.

For telemetry, record HTTP 306, method, authority, route template rather than secrets, response headers relevant to caching or retry, latency, upstream identity, and whether the response originated at the application or an intermediary.


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