The system interface is associated with a network entity (such as a specific Nokia router), not a specific interface. The system interface is also referred to as the loopback address. The system interface is associated during the configuration of the following entities:
Termination point of service tunnels
Hops when configuring MPLS paths and LSPs
Addresses on a target router for BGP and LDP peering
The system interface is used to preserve connectivity (when routing reconvergence is possible) when an interface fails or is removed. The system interface is used as the router identifier. A system interface must have an IP address with a 32-bit subnet mask.