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.