An LDP LSR ID is configured to identify the LDP instance. In an IPv4 network, the related LDP LSR ID is automatically set to the highest IPv4 address associated with the router interface, with loopback addresses taking precedence over VLAN addresses. You must explicitly configure an LDP LSR ID for an IPv6 network.
Use the mpls ldp-lsr-id command in global router configuration mode to configure an LDP LSR ID. The LDP LSR ID is configured in the a.b.c.d format the same as an IPv4 address. The LDP LSR ID is not an address. It is used as an identifier of the LDP instance.