BGP Support for Global Load Balancing in DC Fabric

In a DC fabric, hashing is unable to ensure even load distribution over all ECMP links, which might result in congestions on certain links and underutilization on other links. Dynamic load balancing helps to avoid congested links to mitigate local congestion. However, dynamic load balancing cannot address some congestions. For example, AI ML traffic that has elephant flows and lacks entropy causes congestions in the fabric. In this case, global load balancing (GLB) helps to mitigate these congestions. Global load balancing is hashing a route with multiple ECMP links onto several links for load balancing.

In a CLOS network the congestions on the first two next hops impacts the load balancing decisions of the local node and the previous hop nodes triggering global load balancing. If the route has only one next-next-hop, a simple path quality profile is created. If the route has more than one next next-hop node then a simple path quality profile is created for each next next-hop node.

To enable global load balancing, include the global-load-balancing statement at the [edit protocols bgp] hierarchy level. We have disabled this statement by default.