Equal cost multi-path (ECMP) routing protocol increases the north and south communication bandwidth by adding an uplink to the tier-0 logical router and configure it for each Edge node in an NSX Edge cluster. The ECMP routing paths are used to load balance traffic and provide fault tolerance for failed paths.

The tier-0 logical router must be in active-active mode for ECMP to be available. A maximum of eight ECMP paths are supported. The implementation of ECMP on NSX Edge is based on the 5-tuple of the protocol number, source address, destination address, source port, and destination port. The algorithm used to distribute the data among the ECMP paths is not round robin. Therefore, some paths might carry more traffic than others. Note that if the protocol is IPv6 and the IPv6 header has more than one extension header, ECMP will be based only on the source and destination addresses.

Figure 1. ECMP Routing Topology
Equal cost multi-path routing with two uplinks to the tier-0 logical router of each Edge nose in a cluster.

For example, the topology above shows a single tier-0 logical router in active-active mode running on a 2-node NSX Edge cluster. Two uplink ports are configured, one on each Edge node.