Cisco Technology, Inc.

Mike Shand

David Delano Ward

Stefano Benedetto Previdi

Keyur Patel

Stewart Frederick Bryant

Dino Farinacci

Robert Raszuk

Gargi Nalawade

Joel P Bion

Alex Tweedly

Clarence Filsfils

An apparatus and method as described for constructing a repair path for use in the event of failure of an inter-routing domain connection between respective components in first and second routing domains of a data communications network. The apparatus is arranged to assign a propagatable repair address for use in the event of failure of the inter-routing domain connection and to propagate the repair address via data communications network components other than the inter-routing domain connection.

Constructing a repair path in the event of failure of an inter-routing domain system link

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

An apparatus for providing reachability in a routing domain of a data communications network having as components nodes and links therebetween for a routing domain external destination address is provided. The apparatus is arranged to advertise destination address reachability internally to nodes in the routing domain and associate a reachability category with the internal advertisement of the destination address reachability.

Providing reachability information in a routing domain of an external destination address in a data communications 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.

In one embodiment, an apparatus and method are described for constructing a repair path in the event of non-availability of a routing domain component of a routing domain comprising, as components, links and nodes. The apparatus is arranged to receive respective network repair addresses from each of the far-side and near-side advertising node for use in the event of non-availability of a routing domain component between the advertising node. The apparatus is further arranged to advertise the near-side advertising node network repair address to one or more far-side nodes via a path external to the routing domain.

Constructing a repair path in the event of non-availability of a routing domain

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.

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Cobham, United Kingdom

Mike Shand