ExtremeXOS supports control plane redundancy and hitless failover.
A stack supports control plane redundancy and hitless failover. Hitless failover is supported to the extent that the failing master node and all of its ports are operationally lost, including the loss of supplied power on any PoE (Power over Ethernet) ports that the node provided, but all other nodes and their provided ports continue to operate. After the failover, the backup node becomes the master node.
At failover time, a new backup node is selected from the remaining standby nodes that are configured to be master capable. All operational databases are then synchronized from the new master node to the new backup node. Another hitless failover is possible only after the initial synchronization to the new backup node has completed. This can be seen using the show switch {detail} command on the master node and noting that the new backup node is In Sync.
When a backup node transitions to the master node role, it activates the Management IP interface that is common to the whole stack. If you have correctly configured an alternate management IP address, the IP address remains reachable.
When a standby node is acquired by a master node, the standby node learns the identity of its backup node. The master node synchronizes a minimal subset of its databases with the standby nodes.
When a standby node loses contact with both its acquiring master and backup nodes, it reboots.
A master node that detects the loss of an acquired standby node indicates that the slot the standby node occupied is now empty and flushes its dynamic databases of all information previously learned about the lost standby node.
A backup node restarts if the backup node has not completed its initial synchronization with the master node before the master node is lost. When a backup node transitions to the master node role and detects that the master node has not already synchronized a minimal subset of its databases with a standby node, the standby node is restarted.
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