 MPLS-capable devices are referred to as LSRs.The paths an LSR knows can be defined using explicit hop-by-hop configuration, or are dynamically routed by the constrained shortest path first (CSPF) algorithm, or are configured as a loose route that avoids a particular IP address or that is partly explicit and partly dynamic.In a pure IP network, the shortest path to a destination is chosen even when the path becomes congested.