A network engineer is configuring a newly installed PE router at the regional gateway location.

To establish LDP sessions between the PE and P routers, you need to enable communication over TCP port 646 for T-LDP hello messages.

T-LDP (Targeted LDP) uses TCP port 646 for session establishment.

Example configuration:

interface GigabitEthernet0/0

mpls ldp discovery targeted-hello accept

References:

Implementing and Operating Cisco Service Provider Network Core Technologies (SPCOR) v1.0 course material.