Method and apparatus to improve ldp convergence using hierarchical label stacking

A method in a first network element acting as an egress LSR (Label Switched Router) in an MPLS (Multiprotocol Label Switching) network for originating label mapping messages to establish a hierarchical LSP (Label Switched Path) from a second network element acting as an ingress LSR through a set of one or more third network elements acting as intermediate LSRs to the first network element, the method comprising the steps of:

• generating an egress LSR label mapping message that includes a label mapped to an IP address of the first network element;
• for each one of a plurality of FECs (Forwarding Equivalence Classes) that belong to a plurality of end stations respectively in which the first network element is an egress, generating a hierarchical label mapping message for that FEC that indicates a label originated by the first network element for that FEC and indicates that the first network element originated that label;
• transmitting the egress LSR label mapping message and the hierarchical label mapping messages to one or more peers of the first network element to allow for the establishment of the hierarchical LSP for each of the plurality of FECs that includes an outer LSP that defines a path to reach the first network element and an inner LSP specific to that FEC that is used by the first network element to identify and forward packets to that FEC;
• whereby the hierarchical LSP allows for the second network element to react to a topology change that affects reachability to the first network element through changing one or more forwarding entries associated with the outer LSP without modifying substantially any forwarding entry associated with any of the inner LSPs.

A network element acting as an ingress LSR (Label Switched Router) in an MPLS (Multi-Protocol Label Switching) network to transport packets belonging to end stations across the MPLS network using a hierarchical LSP (Label Switched Path), the network element comprising:

• a control card including an hierarchical label module that is operative to:
• process hierarchical label mapping messages originated from an egress LSR for a plurality of FECs (Forwarding Equivalence Classes) belonging to the end stations that each include a mapping of a label originated by the egress LSR for a FEC and indicates that the egress LSR originated that label, and egress LSR label mapping messages originated from the egress LSR that each include a label mapped to an IP address of the egress LSR, such that a hierarchical LSP is established for each of the plurality of FECs, wherein the hierarchical LSP for each FEC includes:
• an egress LSR LSP based on the egress LSR label mapping message that is common for each of the FECs and provides a next-hop to the egress LSR, and
• a unique FEC LSP that carries information to identify and forward packets to the FEC;
• download one or more forwarding structure entries representing the hierarchical LSP to one or more line cards of the network element;
• and
• responsive to a topology change that changes the next-hop to the egress LSR, modify and download to the one or more line cards one or more forwarding structure entries for the egress LSR LSP to change the next-hop for the egress LSR without modifying and downloading substantially any forwarding structure entries for the FEC LSPs;
• whereby LDP convergence time is improved through a reduction of forwarding structure modifications after the topology change.

A first network element to act as an egress LSR (Label Switched Router) in an MPLS (Multiprotocol Label Switching) network for a plurality of FECs (Forwarding Equivalence Classes) belonging to a plurality of end stations respectively, and to originate label mapping messages to establish a hierarchical LSP (Label Switched Path) from a second network element that acts as an ingress LSR for the FECs through a set of one or more third network elements that act as intermediate LSRs, the first network element comprising:

• a control card including an hierarchical label module that is operative to:
• generate an egress LSR label mapping message that includes a label mapped to an IP address of the first network element,
• for each of the plurality of FECs, generate a hierarchical label mapping message for that FEC that indicates a label originated by the first network element for that FEC and indicates that the first network element originated that label, and
• cause a transmission of the generated egress LSR label mapping message and the hierarchical label mapping message to the set of third network elements to be propagated through the MPLS network to allow for an establishment of a hierarchical LSP for each of the FECs that includes an outer LSP that defines a path to reach the IP address of the first network element and an inner LSP specific to that FEC that is used by the first network element to identify and forward packets to that FEC;
• whereby the hierarchical LSP allows for the second network element to react to a topology change that affects reachability to the first network element through changing one or more forwarding entries associated with the outer LSP without modifying substantially any forwarding entry associated with any of the inner LSPs.