Not all virtual networks are going to be connected to the physical world in the same way; some VXLAN logical switches may need to be directly layer 2 adjacent to an existing VLAN backed network, or need to reach a gateway or service interface that resides on a physically defined VLAN. These are some reasons VLAN to VXLAN bridge(s) may need to be implemented within VMware NSX. This is most common in the case of a migration effort to, or if a layer 2 domain containing workloads attached to both VXLAN and VLAN backed networks required.