ECMP (Equal Cost Multi-Path) is a routing protocol that 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 cluster2. The ECMP routing paths are used to load balance traffic and provide fault tolerance for failed paths2. The tier-0 logical router must be in active-active mode for ECMP to be available2. A maximum of eight ECMP paths are supported2. Configuring ECMP on the tier-0 gateway can address low throughput and congestion by distributing the traffic among multiple paths and avoiding bottlenecks.

Deploying Large size Edge node/s can also address low throughput and congestion by providing more resources (memory, CPU, disk) for the Edge node to handle the network traffic. The NSX Edge VM system requirements vary depending on the appliance size, which affects the bandwidth, NAT/firewall, load balancer, and VPN capabilities of the Edge node1. A Large size Edge node has 32 GB memory, 8 vCPU, 200 GB disk space, and can support 2-10 Gbps bandwidth, L2-L4 features, and L7 load balancer1. An Extra Large size Edge node has 64 GB memory, 16 vCPU, 200 GB disk space, and can support more than 10 Gbps bandwidth, L2-L4 features, L7 load balancer, and VPN1. Deploying a larger size Edge node can improve the performance and capacity of the tier-0 gateway. References: 2: Understanding ECMP Routing - VMware Docs(https://docs.vmware.com/en/VMware-NSX-T-Data-Center/3.2/administration/GUID-443B6B0D-F179-429E-83F3-E136038332E0.html)  1: NSX Edge VM System Requirements - VMware Docs(https://docs.vmware.com/en/VMware-NSX-T-Data-Center/3.2/installation/GUID-22F87CA8-01A9-4F2E-B7DB-9350CA60EA4E.html)