In the default configuration, an SDDC network has a single T0 router through which all North-South traffic flows.

In the default configuration, a single active/passive pair of edges are deployed. This edge deployment supports the default traffic group, which is not configurable. If additional bandwidth is required for a subset of this traffic routed to SDDC group members, a Direct Connect Gateway attached to an SDDC group, or to the connected VPC, the SDDC can be re-configured to be Multi-Edge by creating traffic groups, each traffic group creates an additional T0 router.

A traffic group uses an association map to associate a prefix list of CIDR blocks to one of the T0 gateways that support non-default traffic groups in the SDDC. Prefix lists are independent of gateways and consist of source IP addresses. Traffic from those addresses is routed to the T0 edge that supports the associated traffic group. Prefix lists can be created and updated at any time, but a prefix list cannot be removed if it is included in an association map. Associating a prefix list with a traffic group routes all traffic from CIDR blocks in the list through the T0 router created for the group.

Because edges are deployed in active/passive pairs and no two edges can run on the same ESXi host, at least four ESXi hosts in the first vSphere Cluster are required to create a traffic group.