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Layer 3 VPN Load Balancing Overview

 

The load balancing feature allows a device to divide incoming and outgoing traffic along multiple paths in order to reduce congestion in the network. Load balancing improves the utilization of various network paths, and provides more effective network bandwidth.

When multiple protocols are in use, the device uses the route preference value (also known as the administrative distance value) to select a route. While using a single routing protocol, the router chooses the path with the lowest cost (or metric) to the destination. If the device receives and installs multiple paths with the same route preference and same cost to a destination, load balancing must be configured.

In a network with both internal and external BGP paths installed among devices in different autonomous systems, BGP selects only a single best path by default, and does not perform load balancing. A Layer 3 VPN with internal and external BGP paths uses the multipath statement for protocol-independent load balancing. When you include the multipath statement in a routing instance, protocol-independent load balancing is applied to the default routing table for that routing instance. By using the vpn-unequal-cost statement, protocol-independent load balancing is applied to VPN routes. By using the equal-external-internal statement, protocol-independent load balancing is applied to both internal and external BGP paths and can be configured in conjunction with IP header filtering (enabled with the vrf-table-label statement).