Cisco Technology, Inc.

Joel P Bion

Dino Farinacci

Mike Shand

Alex Tweedly

Pradeep Kumar Kathail

Andrew J Valencia

Carl D Sutton

A data structure is stored in a memory of a router, the router located along a path between a source end station and a plurality of destination end stations in a multicast distribution tree. In response to receipt of trace packets containing a listing of network devices in the multicast distribution tree, the data structure is updated. When the source end station desires to send a multicast packet, it transmits a packet to the router. The router then writes the path information stored in the data structure into the packet. Such path information may include a tree list that specifies the arrangement of network devices along the multicast distribution tree and an address list that specifies the Internet Protocol (IP) addresses of these network devices along the multicast distribution tree. By storing the complete description of the network devices of the multicast distribution tree in the packet, routing demands on the devices along the multicast path are minimized.

Small group multicast in a computer network

A network packet is encapsulated and has at least one field in the header of the encapsulation. A multicast delivery tree is written into a field of the encapsulating header. A method for operating a router to use the multicast delivery tree encapsulated in the header of the network packet has the following steps. The router receives a packet from a computer network, the packet having an encapsulated field. The router then reads a multicast delivery tree from the encapsulated field, the multicast delivery tree having a route to each of a plurality of destination stations. Then, the router forwards the packet to an address selected in response to the multicast delivery tree.

The invention solves the problem of overloading intermediate routers with state information as the number of multicast groups increases to millions of groups. The invention places multicast delivery tree information in the header of an encapsulated multicast packet, thereby relieving the routers from maintaining any state information about the multicast groups. The encapsulated packet is referred to as a small group multicast packet, or SGM packet. Routers which are neither branch points of the delivery tree nor destination routers will also need to do no additional forwarding processing other than that needed for standard unicast forwarding. A protocol designation field in the Layer 3 header informs the router that the packet is a SGM packet, and that the router is therefore instructed to parse the packet for route information. The router parses the SGM packet header and determines the next hop address of routers in the multicast delivery tree. The standard unicast forwarding tables are then consulted to determine the next packet destination addresses, and the router then rewrites the SGM packet and routes it to the next hop router. The routing tables also instruct the router as to which outbound port to route the packet.

A method and system for notifying router subsystems of configuration changes made to router configuration information which are maintained by a centralized information provider or database system. The centralized database provides registration and unregistration for notification of changes made to the router configuration information. The centralized database further provides router configuration change notifications to subsystems registered to receive such notifications.

Subsystem application notification method in a centralized router database

A method and system for maintaining and updating routing information in a packet switching network for a set of quasidynamic routes, in which intermittent routing updates are permitted, so that routes are no longer &ldquo;always static&rdquo; or &ldquo;always dynamic&rdquo;, but may change over time between static and dynamic, and are treated accordingly. The invention is particularly applicable to dial-on-demand serial communication links, but is also useful in any situation where it is desired to reduce the overhead from routing updates over a communication link, or where transmission over a communication link is not reliable. A protocol manager for a dynamic routing protocol is modified to determine, for each route, (1) whether to send updated routing information for that route (at the time it would otherwise send an update for a particular route), and (2) whether to age that route in its routing tables (at the time it would otherwise age that route). The modified protocol manager thus prevents automatic aging of routes, while avoiding the use of manually configured static routing tables. Routing information is thus learned automatically and dynamically at appropriate times, and refreshed periodically so that it eventually reflects actual changes to the network topology.

Snapshot routing

A method and system for maintaining and updating routing information in a packet switching network for a set of quasidynamic routes, in which intermittent routing updates are permitted, so that routes are no longer 'always static' or 'always dynamic', but may change over time between static and dynamic, and are treated accordingly. The invention is particularly applicable to dial-on-demand serial communication links, but is also useful in any situation where it is desired to reduce the overhead from routing updates over a communication link, or where transmission over a communication link is not reliable. A protocol manager for a dynamic routing protocol is modified to determine, for each route, (1) whether to send updated routing information for that route (at the time it would otherwise send an up-date for a particular route), and (2) whether to age that route in its routing tables (at the time it would otherwise age that route). The modified protocol manager thus prevents automatic aging of routes, while avoiding the use of manually configured static routing tables. Routing information is thus learned automatically and dynamically at appropriate times, and refreshed periodically so that it eventually reflects actual changes to the network topology.

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Saratoga, CA, United States of America

Joel P Bion