MPLS LDP

• LSRs uses LDP to send messages to their neighbors.
• By advertising an IP prefix & label in the update, the LSR says:
• if you want to send packets to this prefix, send them(packets) to me"
• Stand for RFC 3036 "LDP specification"
• Neighbor discovery:
• send via UDP port 646 to 224.0.0.5
• Neighbor adjacency
• uses tcp port 646 to remote LDP router-id
• Label advertisement 
• Advertise FEC for
• connected IGP interfaces
• IGP learned routes
• For MPLS unicast ip routing:
• LDP simply advertises labels for each prefix listed in the IP routing table.
• New ip route in the unicast ip routing table triggers the LDP advertisement.
• To learn the new route LSR allocates a label called a local label
• Local Label:
• which represent the ip prefix just added to the routing table.
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