Q: What is the difference between the basic discovery scheme of MPLS LDP and its extended discovery scheme?
1. Extended discovery scheme: The destination address of target hello is the specified IP address, not the mutlicast address 188.8.131.52.
2. The basic discovery scheme is symmetrical, and the extended discovery scheme is asymmetrical. The master LSR transmits target hello to the slave LSR which decides if it responds or discards the packet (Hello message--R bit in common parameters TLV decides it). The slave LSR transmits target hello regularly to the master LSR as response (it means the session could set up if one side transmits target hello).