Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-02-09
2002-09-03
Vu, Huy D. (Department: 2665)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C307S408000
Reexamination Certificate
active
06445710
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to interconnected networks of computers and related devices and, more particularly, to techniques facilitating communication between stations connected to widely separated local area networks (LANs). A local area network includes a set of stations or nodes connected to a common communication bus or ring. Typically, all elements of a single LAN are located in a single building or group of buildings. Multiple LANs are often connected together by devices called bridges, to form an extended LAN. A bridge is a device that is connected to more than one LAN, that “listens” to message traffic on each of its LANs, and that forwards the traffic onto selected other LANs. The bridge message forwarding operation is limited by a spanning tree algorithm in which all bridges participate. Messages are forwarded only over a loop-free spanning tree, to avoid closed loops and multiple copies of messages. Message forwarding is further controlled by the bridge's “learning” function. Each bridge learns the directional locations of various stations that are the sources of messages it hears, and “remembers” these locations for future use in forwarding message traffic.
Multiple LANs and extended LANs may also be interconnected to form wide area networks (WANs). The mechanism through which extended LANs are interconnected is typically through devices such as routers. At a broad conceptual level, routers perform a similar task to bridges in that each router is connected to multiple LANs or extended LANs. However, the router operates at a different protocol layer (known as the network layer), and a router can be used for forwarding traffic only if the source of the traffic cooperates by using a network layer protocol that is understood by the router. A bridge, on the other hand, is a packet switch that is “transparent.” A station that does not have a network layer protocol, or has a network layer protocol that is not implemented by the router, can use the bridge as a packet switch. Unfortunately, however, bridges have significant drawbacks that preclude their use in many contexts.
The most significant drawback of a bridge, as compared with a router, is that bridges use only a subset of the actual topology of the interconnected networks. In particular, redundant paths cannot be used, because to do so would result in closed loops and unwanted multiplication of message traffic. As already mentioned, to ensure a loop-free topology, bridges participate in a spanning tree algorithm, which establishes a loop-free tree structure. If two extended LANs were to be interconnected by a bridge, the separate spanning trees of the two networks would have to be combined, forming one larger extended LAN. This might not be desirable from a network administration standpoint. Another important disadvantage of bridges is that they cannot forward traffic through a router, because the packets handled by the bridge do not necessarily have the appropriate network layer information needed to utilize the router. Also, since routers do not participate in the spanning tree algorithm, there is a possibility of forming loops in the topology if bridges were to forward traffic through routers.
In summary, neither routers nor bridges provide an ideal solution to the problems of forwarding message traffic over wide-area networks. Some communication protocols cannot work through routers, since routers support only certain network layer protocols. But bridges are limited, by the spanning tree algorithm, to a subset of the overall network topology, and cannot be used to forward traffic through routers that separate LANs. U.S. Pat. No. 5,150,360 issued Sep. 22, 1992, entitled “Utilization of Redundant Links in Bridged Networks” (which is owned by the assignee of the present application), provides for the establishment of point-to-links outside the spanning tree, but still does not permit forwarding of traffic through traditional routers.
What is needed is a new approach that permits traffic to be forwarded transparently across WANs, using more optimal routes and permitting the traffic to traverse traditional routers. The present invention satisfies this need.
Another way of viewing the problem that this invention solves is that, ideally, there should be some way to address messages directly to particular extended LANs. However, the addressing conventions that have evolved for interconnected networks do not include any convenient means for addressing extended LANs. What is needed then, is some way of forwarding a message more directly to the extended LAN in which the message destination is located. The present invention also satisfies this need.
SUMMARY OF THE INVENTION
The present invention resides in a method and apparatus for logically interconnecting local area networks and extended local area networks, even if they are separated by wide area networks having traditional routers.
Briefly, the method of the invention includes the steps of providing a number of devices with the capability to form “tunnels” between LANs that may be widely separated, these special devices being referred to as tunnelers; then electing a unique designated tunneler for each LAN (LAN) for which tunneling is to be provided. Each LAN has no more than one designated tunneler, but a single tunneler may be designated by more than one LAN. The next steps are configuring the tunnelers, by supplying each with information identifying other tunnelers with which a tunnel may be established, establishing at least one tunnel between two designated tunnelers by exchanging messages between the two tunnelers, if the configuration rules state that such a tunnel should exist, and then selectively forwarding message traffic through the established tunnel, from one LAN to another.
In a preferred embodiment of the invention, the step of electing a unique designated tunneler for each LAN includes executing a spanning tree algorithm among all of the devices connected to the LAN, thereby electing a root device. Since not all devices will necessarily have tunnel capability, some adjustment may be needed to device priorities used in the spanning tree algorithm, to ensure that the root device does have tunneling capability. In this way, the election of a designated tunneler is conveniently effected by means of the existing spanning tree algorithm.
The step of configuring the tunnelers includes supplying to each tunneler the identities of other tunnelers and the identities of ports through which the other tunnelers are connected to LANs with which the ports are associated. The step of establishing a tunnel includes transmitting a greeting from a designated tunneler to each other tunneler that is a potential tunnel endpoint, receiving a message from one of the potential tunnel endpoints confirming that a tunnel may be established, and recording the successful establishment of a tunnel. Establishing a tunnel may also include the steps of transmitting a greeting to at least one backup tunneler, after failing to receive a confirming message from the other designated tunneler; then receiving a message from the backup tunneler confirming that a tunnel may be established; and finally recording the successful establishment of the tunnel. The step of selectively forwarding message traffic through the established tunnel includes the steps of receiving a message at a tunneler, and determining whether the message destination is known to the tunneler. If the destination is known, the method further includes the steps of determining whether a tunnel is required to reach this particular destination, and, if so, forwarding the message through the tunnel, if the tunnel has been established and the message is of a type authorized for forwarding through the tunnel.
If the destination is not known, a subsequent step in the method is determining whether the message was received from a tunnel. If so, the message is forwarded through a port defined as the tunnel endpoint. If the message was not received from a tunnel and the message destination is not
Harper John
Hawe William R.
Perlman Radia Joy
Enterasys Networks Inc.
Nguyen Toan
Vu Huy D.
Wolf Greenfield & Sacks P.C.
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