LDP Neighbor Discovery - Components and Process

LDP Neighbor Discovery


LDP uses which two components to discover neighbors on a network segment? (Choose two.)



Click on the arrows to vote for the correct answer

A. B. C. D. E. F. G.



LDP (Label Distribution Protocol) is a protocol used by MPLS (Multiprotocol Label Switching) to establish and maintain label-switched paths (LSPs) through a network.

LDP discovers neighbors on a network segment using two components:

  1. LDP Hellos: LDP Hellos are multicast messages sent by LDP-enabled devices to the "All LDP Routers" multicast address ( on a network segment. The Hellos are used to establish and maintain LDP neighbor relationships between devices. When a device receives an LDP Hello, it responds with its own Hello to establish the neighbor relationship.

  2. TCP Connection: After the Hellos have been exchanged, the devices establish a TCP connection on port 646 between themselves to exchange LDP messages. LDP uses TCP for reliability, sequencing, and flow control of its messages. The LDP messages exchanged between the neighbors include label mapping, label release, and label withdraw messages.

Therefore, the correct options are B (646 udp port) and C (646 tcp port). Options A ( multicast address), D ( multicast address), E (711 tcp port), and F (711 udp port) are not used by LDP for neighbor discovery. Option G ( multicast address) is used for LDP Hello messages, but it is not listed as an option in the question.