How it works...

When CDO mode is enabled in a transport zone, it will create a hidden logical switch called a CDO logical switch to handle BUM traffic when the control plane connectivity is lost. The CDO logical switch creates a Global VTEP, which is maintained by all ESXi hosts. All ESXi hosts in the transport zone join the CDO logical switch, and one of the NSX controller nodes will be responsible for updating the Global VTEP information to all hosts on the vSphere cluster associated to that transport zone. The Global VTEP information is populated when the control plane connectivity is up and utilized when the control plane connectivity is lost so the BUM traffic can still be handled.

The BUM traffic is replicated to the entire transport zone via the CDO logical switch. No issues will arise when powering on a VM or vMotioning a VM to a new host, as the Global VTEP list information will be used:

The CDO logical switch takes the next available segment ID from the segment ID pool to be the CDO logical switch. In our example recipe, the latest logical switch uses the segment ID 10003 and when CDO mode is enabled, the CDO logical switch uses the segment ID 10004. If a new normal logical switch is created, it would use the segment ID 100002 and skip the segment ID 10005, as shown in the following diagram: