13.5.1 End-to-end and Hop-by-hop Headers
For the purpose of defining the behavior of caches and non-caching proxies, we divide HTTP headers into two
categories:
· End-to-end headers, which are transmitted to the ultimate recipient of a request or response. End-to-end
headers in responses MUST be stored as part of a cache entry and MUST be transmitted in any response
formed from a cache entry.
· Hop-by-hop headers, which are meaningful only for a single transport-level connection, and are not stored
by caches or forwarded by proxies.
The following HTTP/1.1 headers are hop-by-hop headers:
· Connection
· Keep-Alive
· Proxy-Authenticate
· Proxy-Authorization
· TE
· Trailers
· Transfer-Encoding
· Upgrade
All other headers defined by HTTP/1.1 are end-to-end headers.
Other hop-by-hop headers MUST be listed in a Connection header, (section 14.10) to be introduced into
HTTP/1.1 (or later).