Load Sharing

When more than one path exists between the source and destination, load sharing often becomes an important factor for better bandwidth utilization. You can deploy load sharing in many different ways. Load sharing is sometimes completely transparent to pseudowire traffic if it only involves core routers in the network. The case studies in this section focus on the load-sharing scenarios that involve provider edge (PE) routers performing pseudowire emulation over MPLS. More precisely, an ingress PE router sees more than one path to reach the egress PE router for pseudowire traffic.

Service providers normally deploy standard-based routing protocols in the core networks, such as Open Shortest Path First (OSPF) and Intermediate System-to-Intermediate System (IS-IS), which support Equal-Cost Multipath (ECMP) load sharing. With these routing protocols, only routes that have the least cost to a given destination are shown in the forwarding table. If multiple equal-cost routes go to the same destination, all of them are installed in the forwarding table. Depending on the traffic type and forwarding configuration, packets with the same destination are distributed across these paths.