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.
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.
North-Bound ECMP Routing
To ensure optimal network performance when using north-bound ECMP routing, we recommend configuring Tier-1 and Tier-0 as follows:
Case 1: Connect Tier-1 to Tier-0 and select the same edge cluster for both Tier routers. This will ensure that all traffic from Tier-1 to Tier-0 is evenly distributed across all uplinks.
Case 2: Create an additional uplink for Tier-0. This will diversify the usage of Tier-0 uplinks, ensuring that no single uplink is overloaded.
The number of edge nodes in Tier-0 cluster (used by Tier-1's ECMP) should not be the same as the number of Tier-0 uplinks (used by Tier-0's ECMP). This ensures a more balanced distribution of traffic across the network, improving overall network efficiency.
