Relayed CSPF Computation for Multiple Areas and Multiple Autonomous Systems

A method in a router for participating in computation of a constraint-based label switched path (LSP) that spans a plurality of areas to reach a destination, wherein the router resides in a first one of the plurality of areas and the destination is in the first area, the method comprising the steps of:

• receiving a path computation request message from a router residing in a second one of the areas, the path computation request message including a set of one or more attributes for each of a set of one or more path segments that were computed by the router in the second area to a set of one or more border routers;
• computing a set of one or more path segments to the destination using the set of attributes for each of the set of path segments computed by the router residing in the second area;
• and
• transmitting a path computation reply message to the router residing in the second area, the path computation reply message specifying the set of computed path segments to the destination and a set of one or more attributes for each computed path segment to the destination.

An apparatus to participate in computation of a constraint-based label switched path (LSP) that spans a plurality of areas to reach a destination, the apparatus comprising:

• a router configured to perform the following:
• compute a path segment that meets a set of one or more constraints to at least one border router of the first area, wherein the at least one border router lies in a path necessary to reach the destination;
• transmit a path computation request message to a path computation element in a second one of the plurality of areas, wherein the path computation request message includes a set of one or more attributes for each computed path segment that are used by the path computation element to compute one or more path segments towards the destination of the constraint-based LSP;
• receive a path computation reply message from the path computation element that specifies a set of one or more computed path segments that meet the set of constraints and that were computed by one or more path computation elements downstream from the router;
• and
• stitch at least one of the set of computed path segments that are specified in the path computation reply message with the path segment computed by the router to form at least part of the constraint-based LSP.

An apparatus to participate in computation of a constraint-based label switched path (LSP) that spans a plurality of areas to reach a destination, the apparatus comprising:

• a router configured to perform the following:
• receive a path computation request message from a router residing in a second one of the areas, the path computation request message to include a set of one or more attributes for each of a set of one or more path segments that were computed by the router in the second area to a set of one or more border routers;
• compute a set of one or more path segments to the destination using the set of attributes for each of the set of path segments computed by the router residing in the second area;
• and
• transmit a path computation reply message to the router residing in the second area, the path computation reply message to specify the set of computed path segments to the destination and a set of one or more attributes for each computed path segment to the destination.