In a client/server computing environment a need may arise to enable a client to communicate with two servers, each of which provide functions that represent a portion of a service desired by the client. In some cases, it is desirable to permit the client to communicate with only a first one of the two servers and to prevent direct contact between the client and the other of the two servers.
FIG. 1 is a block diagram of a networked computer system in which the foregoing general problem may arise. Client 102 is a computer device such as a workstation, server, router, or switch. Client 102 is coupled to network 104, which is an interconnected combination of computers, terminals, or peripherals used to provide communications between two or more points. A first server 106 and a second server 108 are coupled to network 104, logically separated from client 102. In one embodiment, client 102, network 104, and servers 106, 108 communicate using TCP/IP network protocols, and using HTTP protocol messages that comprise requests and responses. Such protocols are exemplary and not required.
Client 102 may communicate an HTTP request for a service to network 104. The request includes a name or other identifier of server 106, which client 102 expects to provide the requested service. Network 104 locates server 106 and routes the request to server 106, thereby establishing a logical connection 110 from client 102 to the server. Server 106 determines that it cannot provide the function or service solicited in the request, but that server 108 can provide the function or service. Accordingly, software elements in server 106 automatically divert or “redirect” the request to server 108 over a logical connection 112, which may physically travel through the network 104. Server 108 processes the request, generates a response message, and sends the response message back to client 102 over logical connection 114, which may pass through network 104.
In this scenario, when the client and the servers use HTTP, the response message may include a document formatted using a structured markup language, such as HTML. The HTML document may contain hyperlinks or other references to resources within server 108, or other servers or network elements. As a result, client 102 may select one of the hyperlinks or references, and thereby attempt to request a service of server 108 directly along connection 114. Server 106 would not be involved in processing such a request.
This result is undesirable in several circumstances. The server 106 may have been designated as authoritative for certain kinds of transactions. The server 106 may have redirected the original request to server 108 solely because server 106 cannot directly process the request, whereas server 108 can, but server 106 may need to remain in control of the overall transaction. For example, server 106 may have redirected the original request to server 108 just to carry out a specialized or subordinate task, although server 106 remains responsible for the total transaction or for presenting a consistent interface to the client 102.
Accordingly, there is a need in this field for a mechanism that allows a client request to be redirected from a first server to a second server, while keeping the first server in control of subsequent requests by the client for services of the second server.
In particular, there is a need for a mechanism that prevents the client from directly communicating with the second server even after the first server has redirected a request of the client to the second server.
There is a specific need in Internet protocol networks, such as Intranets or the Internet in which clients and servers use TCP/IP and HTTP, to force subsequent requests resulting from HTML generated by the second server to come back to the first server for further redirection.