Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-10-13
2003-09-23
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S218000, C370S242000, C709S203000
Reexamination Certificate
active
06625152
ABSTRACT:
BACKGROUND OF THE INVENTION
A typical data communications network includes multiple host computers (or hosts) which communicate with each other through a system of data communications devices (e.g., bridges, switches and routers) and transmission media (e.g., electrical cable, fiber-optic cable, and/or wireless connections). In general, a sending host exchanges data with a receiving host by packaging the data using a standard format or protocol to form one or more data-carrying structures (e.g., packets, frames or cells). The sending host then transfers these structures (hereinafter generally referred to as packets) to the receiving host through the above-described system of data communications devices and transmission media. The receiving host then unpackages and uses the data.
Some network arrangements allow hosts to communicate in a client/server manner. That is, one host operates as a client by sending a client request for a particular service to another host which operates as a server. The client request typically takes the form of one or more packets. In general, each of these client request packets includes, in a destination address field, a device address that uniquely identifies the server among the devices on the network. When the client sends the client request packets over the network, data communications devices positioned between the client and the server transfer the client request packets from the client to the server along some optimized network path based on the device address in the destination address field of each packet.
When the server receives the client request packets, the server typically authenticates the client request, provides the requested service (e.g., records a transaction), and sends a reply or confirmation (e.g., one or more reply packets) back to the client. Again, the data communications devices route the reply packets back to the client based on a device address, which identifies the client, in a destination address field of each packet forming the reply.
A server installation is a server configuration formed by one or more servers. To increase capacity at the server installation (i.e., in order to better service large volumes of client requests), it is tempting to increase the number of servers at the server installation. In one arrangement, one or more servers are added to the server installation. In this arrangement, the multiple servers are arranged to “load share” the volume of client requests. That is, each server is configured to independently handle (or share) a particular portion of the load of client requests. If further capacity is required, the server installation can be scaled yet again by adding one or more additional servers in the same load sharing manner. With such an arrangement, it is important to prevent the possibility of two or more load sharing servers in the above-described server installation from providing the same service in response to a single client request.
Another environment which provides load balancing and fault tolerance is a conventional IBM Mainframe environment. In this environment, a source route bridged (SRB), token ring LAN network is used to connect a network of client workstations to a communications controller. One or more of these communications controllers is then attached to the mainframe server computer.
In order to provide load balancing and fault tolerance in this environment, it is common for there to be multiple communications controllers, connected to different rings with the same media access control (MAC) layer address. When a client workstation wishes to connect to the mainframe server, it typically will transmit an “explorer” TEST frame on the token ring. The SRB network, which consists of a number of token ring LAN segments connected by source route bridges, forward the TEST explorer on all the rings of the network, including the multiple rings that contain the communications controllers configured with the server MAC address. One or more of these communications controllers will respond to the TEST explorer and the reply will be transmitted back through the SRB network to the client workstation.
Typically, the first reply that is received by the client workstation will be used. This reply contains a routing information field (RIF) that specifies a path through the SRB network back to the communications controller which sent it. Data packets that are then sent from the client workstation to the communications controller and back again contain this RIF along with the MAC addresses of the client workstation and communications controller. The combination uniquely identifies one of the multiple communications controllers that have the duplicate server MAC addresses.
Using this system, any number of communications controllers can have the same server MAC address as long as they are on different token ring LAN segments with different ring numbers. The client workstation only needs to know a single MAC address to reach any one of these controllers. If more controllers are added, or some are removed, there is no need for the client workstation configuration to be changed. The explorer TEST frames will always find one if one is available.
Networks may further include other specialized devices to coordinate network traffic in an organized fashion. For example, an Internet Protocol (IP) network may include a load director which physically separates two areas of the IP network. During operation, the load director attempts to reduce unnecessary network traffic in each of the two areas by filtering packets based on their IP source addresses. That is, the load director allows certain packets having particular IP source addresses to pass from one area to the other, while blocking passage of other packets having other IP source addresses. Accordingly, each network area is not deluged with unnecessary packets from the other network area. A manufacturer of such a load director is Cisco Systems of San Jose, Calif.
SUMMARY OF THE INVENTION
Due to a variety of technical and economic factors, the cost of implementing an Ethernet based LAN has become much less than the cost of implementing a token ring LAN. Ethernet LANs typically do not use SRB. They typically use transparent bridging to connect Ethernet LAN segments together. Transparently bridged LAN networks do not support multiple devices with the same MAC address. If 2 or more devices on a transparently bridged LAN have the same MAC address, it is an error that must be fixed in order for the LAN to operate properly. This means that the technique described above for providing fault tolerance and load balancing using duplicate MAC addresses cannot be used on a transparently bridged LAN and we must find an alternative.
The invention provides a way for transparently bridged LANs to achieve the same type fault tolerance and load balancing as the source route bridged LAN described above. In particular, the present invention is directed to techniques which enable a server installation to service a client request using a filter index that is different than a destination address associated with the client request. In such an arrangement, a client can generate a client request for a server installation having multiple servers in the same manner as it would for a server installation having a single server. Accordingly, when a server installation is scaled by increasing the number of servers, reconfiguration of the clients utilizing a server of the server installation is unnecessary.
In one embodiment, the data resides in a data structure having (i) a device identifier that uniquely identifies the server host installation (or simply server host) among multiple server hosts, and (ii) a filter index which is different than the device identifier. In this arrangement, a first filtering data communications device receives the data structure. If the filter index of the data structure complies with a first set of filtering criteria residing in the first filtering data communications device, the first filtering device transfers the data structure from the first filte
Berl Steven
Monsen Robert
Waclawsky John G.
Chapin & Huang , L.L.C.
Cisco Technology Inc.
Huang, Esq. David E.
Waxman Andrew M.
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