# MPLS Interfaces and Labels

When a layer 2 interface is added to a load-balancing group circuit, an MPLS shim interface is automatically created on top of that layer 2 interface. The attributes of the shim interface are inherited from the load-balancing group and cannot be configured.

All MPLS shim interfaces within a load-balancing group circuit point to the same MPLS next hop. Traffic arriving from the CE router over this set of MPLS shim interfaces is merged into a single LSP and sent to the remote PE router.

The VC in label for the layer 2 circuit points to a single ECMP MPLS next hop. The legs of this ECMP next hop are the member shim interfaces of the load-balancing group circuit. Consequently, ECMP is used to forward traffic arriving from the core across the MPLS shim interfaces to the CE router.