Patent ID: 8223629

Claim:
A routing method in a first autonomous system, the first autonomous system comprising a core router connected to nominal output routers adapted to route traffic whose destination is a second autonomous system, the first autonomous system further including at least one back-up output router adapted to route traffic whose destination is the second autonomous system, the method comprising: identifying, by the core router, a router of the first autonomous system which is adapted to route traffic whose destination is the second autonomous system in the event of failure affecting traffic at least one of the nominal output routers; exchanging, for each of the nominal output routers, a contextual label between the core router and the identified router; installing a routing table in the core router which includes, for a destination of the second autonomous system, for each of the nominal output routers, a nominal output to the nominal output router, and a back-up output to a predetermined route in a tunnel beginning at the core router and ending at the identified router but which does not pass through the nominal output routers; and installing, for each exchanged contextual label, a contextual routing table associated with the contextual label in the identified router, the contextual routing table including, for a destination of the second autonomous system, at least one route which does not pass through the nominal output router, wherein, for each of the nominal output routers, the core router performs: detecting whether there is a failure affecting routing of traffic to the nominal output router; activating the nominal output of the routing table of the core router, if no failure is detected; and activating the back-up output of the routing table of the core router, if a failure is detected, and adding the exchanged contextual label associated with the nominal output router to each packet of the traffic sent in the tunnel, and wherein the identified router routes packets whose destination is the second autonomous system received with one of the exchanged contextual labels using the contextual routing table associated with the exchanged contextual label.