8.1.3 Proxy Servers

   It is especially important that proxies correctly implement the
   properties of the Connection header field as specified in 14.2.1.

   The proxy server MUST signal persistent connections separately with
   its clients and the origin servers (or other proxy servers) that it
   connects to. Each persistent connection applies to only one transport
   link.

   A proxy server MUST NOT establish a persistent connection with an
   HTTP/1.0 client.

8.1.4 Practical Considerations

   Servers will usually have some time-out value beyond which they will
   no longer maintain an inactive connection. Proxy servers might make
   this a higher value since it is likely that the client will be making
   more connections through the same server. The use of persistent
   connections places no requirements on the length of this time-out for
   either the client or the server.

   When a client or server wishes to time-out it SHOULD issue a graceful
   close on the transport connection. Clients and servers SHOULD both
   constantly watch for the other side of the transport close, and
   respond to it as appropriate. If a client or server does not detect
   the other side's close promptly it could cause unnecessary resource
   drain on the network.

   A client, server, or proxy MAY close the transport connection at any
   time. For example, a client MAY have started to send a new request at
   the same time that the server has decided to close the "idle"
   connection. From the server's point of view, the connection is being
   closed while it was idle, but from the client's point of view, a
   request is in progress.

   This means that clients, servers, and proxies MUST be able to recover
   from asynchronous close events. Client software SHOULD reopen the
   transport connection and retransmit the aborted request without user
   interaction so long as the request method is idempotent (see section



Fielding, et. al.           Standards Track                    [Page 45]

RFC 2068                        HTTP/1.1                    January 1997


   9.1.2); other methods MUST NOT be automatically retried, although
   user agents MAY offer a human operator the choice of retrying the
   request.

   However, this automatic retry SHOULD NOT be repeated if the second
   request fails.

   Servers SHOULD always respond to at least one request per connection,
   if at all possible. Servers SHOULD NOT close a connection in the
   middle of transmitting a response, unless a network or client failure
   is suspected.

   Clients that use persistent connections SHOULD limit the number of
   simultaneous connections that they maintain to a given server. A
   single-user client SHOULD maintain AT MOST 2 connections with any
   server or proxy. A proxy SHOULD use up to 2*N connections to another
   server or proxy, where N is the number of simultaneously active
   users. These guidelines are intended to improve HTTP response times
   and avoid congestion of the Internet or other networks.