# Understanding CE Load Balancing for Martini Layer 2 Transport

For layer 2 circuits over an MPLS core, each circuit normally has a single shim interface on the local router. In the case of a local cross-connects configuration, each end of the cross-connect has a single shim interface, creating a two-way cross-connect.

Alternatively, a given layer 2 circuit or each end of a local cross-connect can have many shim interfaces. In these cases, traffic destined for the CE routers is load-balanced among the multiple shim interfaces. This is known as CE-side load balancing. In the case of Ethernet/VLANs, CE-side load balancing enables an E Series router to interoperate with an 802.3ad switch.

You can configure load balancing in two different ways. You can configure many shim interfaces with the same peer, VC type, and VC ID. Alternatively, you can use the legacy method of configuring Martini circuits into load-balancing groups.