LDP signaled LSPs for external prefixes Ina Minei, Nischal Sheth - Juniper Luyuan Fang – AT&T

The problem  LDP relies on routing protocols for its forwarding decisions.  To establish LSPs, LDP needs routing table entries for all its FECs.  Not always desirable…

The goal  Establish LSPs for FECs that are “external” to the routing table.  Thus, no need to inject external routes corresponding to the LDP FECs in the IGP just for the purpose of LSP establishment.

Before we start…  The discussion is only for address prefix FECs and host FECs associated with IPv4/IPv6 prefixes.

The idea  If LSRa is the one who is injecting FECa into LDP, can use LSRa’s address in the forwarding decision making process.  Don’t need FECa’s address in the routing table, only need LSRa’s address.

The concepts 1. Decouple the FEC from the routing table entry. 2. Specify a different address on which to apply the decision making process of whether to use the label for forwarding and whether to propagate the FEC to the neighbors.

LDP extensions 1. New TLV (Originator Nexthop TLV) specifying the address to use in the forwarding-state decision-making process. 2. Extensions to the message handling procedures to take advantage of the new TLV.

Originator Nexthop TLV 1. Carries a host address 2. Always shows up together with the FEC TLV 3. Used in label map, withdraw, release messages.

Label mapping procedures Existing algorithm  Conditions for using a label for forwarding: 1. the routing table contains an _exact_ entry for the address in the FEC TLV 2. the mapping was received from the neighbor that is the nexthop for the route found in (1).

Label mapping procedures Extension to the algorithm  Conditions for using a label for forwarding if the label-map message contains the Originator Nexthop TLV: 1. the routing table contains an _exact_ entry for the address in the Originator TLV. 2. the mapping was received from the neighbor that is the nexthop for the route found in (1).

Label withdraw/release Extension to the algorithm  If the label-map message contained the Originator Nexthop TLV then the withdraw/release must also contain it.

What next?  Gauge interest  Please send comments to the list.  Accept as WG document?

Thank you!