LDP sessions: IPv6

IPv6 connectivity often relies on tunneling IPv6 over an IPv4 MPLS core with IPv4-signaled MPLS label-switched paths (LSPs). This requires the IPv4-signaled LSPs to be configured statically or established dynamically by IPv6 provider edge routers. Because of the growing demand of IPv6, it has become imperative to deploy an IPv6 MPLS core with an IPv6-signaled LSP to provide IPv6 connectivity. The network device normally supports LDP in an IPv6 network only, and also in an IPv6/IPv4 dual-stack network as described in RFC 7552. Apart from providing a single session for both IPv4 and IPv6 networks, LDP supports separate IPv4 sessions for IPv4 only, and IPv6 sessions for IPv6 only. 

By default, IPv6 is used as the TCP transport for an LDP session with its peers when both IPv4 and IPv6 are enabled. Additionally, the device allows LDP to establish the TCP connection over IPv4 with IPv4 neighbors, and over IPv6 with IPv6 neighbors as a single-stack label-switching router (LSR). In a such deployment, you must configure one 32-bit long LSR ID for IPv4 TCP sessions and another 32-bit long LSR ID for IPv6 TCP sessions. These two LSR IDs must be nonzero and must be configured with different values.