LDP signaled LSPs for external prefixes

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LDP signaled LSPs for external prefixes
Ina Minei, Nischal Sheth - Juniper
ina_at_juniper.net, nsheth_at_juniper.net Luyuan Fang
ATT luyuanfang_at_att.com

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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

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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.

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Before we start

• The discussion is only for address prefix FECs
  and host FECs associated with IPv4/IPv6 prefixes.

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The idea

• If LSRa is the one who is injecting FECa into
  LDP, can use LSRas address in the forwarding
  decision making process.
• Dont need FECas address in the routing table,
  only need LSRas address.

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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.

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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.

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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.

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Label mapping procedures

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

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Label mapping procedures

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

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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.

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What next?

• Gauge interest
• Please send comments to the list.
• Accept as WG document?

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Thank you!