A cloud deployment or a virtual data center has a variety of applications across multiple tenants. These applications and tenants require isolation from each other for security, fault isolation, and avoiding overlapping IP addressing issues. The NSX logical switch creates logical broadcast domains or segments to which an application or tenant virtual machine can be logically wired. This allows for flexibility and speed of deployment while still providing all the characteristics of a physical network's broadcast domains (VLANs) without physical Layer 2 sprawl or spanning tree issues.
A logical switch is distributed and can span arbitrarily large compute clusters. This allows for virtual machine mobility (vMotion) within the datacenter without limitations of the physical Layer 2 (VLAN) boundary. The physical infrastructure does not have to deal with MAC/FIB table limits since the logical switch contains the broadcast domain in software.
A logical switch is mapped to a unique VXLAN, which encapsulates the virtual machine traffic and carries it over the physical IP network.
The NSX controller is the central control point for all logical switches within a network and maintains information of all virtual machines, hosts, logical switches, and VXLANs. The controller supports two new logical switch control plane modes, Unicast and Hybrid, These modes decouple NSX from the physical network. VXLANs no longer require the physical network to support multicast in order to handle the Broadcast, Unknown unicast, and Multicast (BUM) traffic within a logical switch. The unicast mode replicates all the BUM traffic locally on the host and requires no physical network configuration. In the hybrid mode, some of the BUM traffic replication is offloaded to the first hop physical switch to achieve better performance. This mode requires IGMP snooping to be turned on the first hop physical switch. Virtual machines within a logical switch can use and send any type of traffic including IPv6 and multicast.
You can extend a logical switch to a physical device by adding an L2 bridge. See L2 Bridges.
You must have the Super Administrator or Enterprise Administrator role permissions to manage logical switches.