Controller Disconnected Operation (CDO) mode ensures that the data plane connectivity is unaffected in a multi-site environment, when the primary site loses connectivity. You can enable the CDO mode on the secondary site to avoid temporary connectivity issues related to the data plane, when the primary site is down or not reachable. You can also enable the CDO mode on the primary site for the control plane failure.
CDO mode avoids the connectivity issues during the following failure scenarios:
- The complete primary site of a cross-vCenter NSX environment is down.
- WAN is down.
- Control plane failure.
The CDO mode is disabled by default.
When the CDO mode is enabled and host detects a control plane failure, the host waits for the configured time period and then enters the CDO mode. You can configure the time period for which you want the host to wait before entering the CDO mode. By default, the wait time is five minutes.
NSX Manager creates a special CDO logical switch (4999) on the controller. The VXLAN Network Identifier (VNI) of the special CDO logical switch is unique from all other logical switches. When the CDO mode is enabled, one controller in the cluster is responsible for collecting all the VTEP information reported from all transport nodes, and replicating the updated VTEP information to all other transport nodes. After detecting the CDO mode, broadcast packets like ARP/GARP and RARP is sent to the global VTEP list. This allows to vMotion the VMs across the vCenter Servers without any data plane connectivity issues.
When you disable the CDO mode, NSX Manager removes the CDO logical switch from the controller.
