Configuring the DAD process for replacing logical chassis cluster switches
Use the following procedure to configure DHCP Automatic Deployment (DAD) when replacing switches in logical chassis cluster mode.
For logical chassis cluster switches, the DAD process applies to a new switch and the principal switch.
- Disconnect the existing switch from the cluster.
- Connect the new switch to the cluster. The new switch must be the same model and use the same cable connection as the old switch. The new switch must successfully load Network OS. Note, however, that the new switch cannot join the cluster just yet.
- From the principal switch, manually run the node replacement with the WWN and RBridge ID.
Establish a DAD environment for the new switch. (Make sure DHCP is enabled on the management interface.)
- The management interface of the switch must be set up as DHCP. After setting up the management interface on a switch in fabric cluster mode, you must use the copy running-config startup-config command for the configuration to take effect.
- The DHCP server must have the FTP server IP address and configuration file path.
- The configuration file is on the FTP server and it contains the firmware path, new configuration file path, VCS ID, VCS mode, and RBridge ID.
- The DHCP server and FTP server must be up and running.
- DAD must be enabled on the switch by means of the CLI.
- Enable DAD by using the dhcp auto-deployment enable command, and enter yes when prompted to reboot the system. After the new switch is rebooted, the DAD process downloads the DAD configuration file to get the VCS mode, VCS ID, and RBridge ID. The RBridge ID must be configured the same as the previous node in the cluster. The DAD process sets the VCS ID and RBridge ID for a switch in logical chassis cluster mode. No reboot is triggered. The DAD process invokes a firmware download if new firmware is detected. Firmware download completes successfully and the switch comes up with the new firmware and configuration settings. Note that the DAD process aborts if any error is detected. When the new switch comes up, it joins the cluster with the same configuration as the previous switch.
- Use the show dadstatus command to view the current DAD configuration.
Considerations for enabling DHCP auto-deployment
The dhcp auto-deployment enable command causes a cold/disruptive reboot and requires that Telnet, secure Telnet, or SSH sessions be restarted.
- Scenario 1: When you enable DAD and the system starts to reboot, the DAD process is triggered after configuration replay is complete.
For dual management module (MM) chassis (VDX 8770 chassis), the DAD process waits for the dual MM to be in sync before starting the requested firmware download. However, if you manually issue firmwaredownload - sb during this period (after DAD is triggered and before MM is in sync), DAD fails because the previous firmware download takes precedence. If you manually issue firmwaredownload -sb before DAD is triggered, DAD will fail for the same reason.
- Scenario 2: You issue the command to enable DAD (answer "Yes" when prompted), but before the system reboot, there is an HA failover. DAD will be cancelled. You must enable DAD from the new active switch.
- Scenario 3: You issue the command to enable DAD, but after the system reboot is invoked, takeover occurs (the previous standby switch becomes the new active switch), DAD will proceed.
Scenario 4: You manually issue the firmwaredownload command, but before the firmware download is completed, you enable DAD from the CLI and answer "Yes" when prompted to reboot the switch. When the switch boots up, even if the DAD process detects that the firmware download is needed, it will fail during the sanity check because the previous incomplete firmware download takes precedence. DAD fails.
Scenario 5: If you do not power down the secondary node when running DAD on the principal node, the following outcomes are observed:
The DAD principal node and secondary node form the cluster, but without the principal role. DAD fails on the principal node.
The DAD principal node and secondary node form the cluster with the principal role. DAD proceeds on the principal node because the secondary node does not affect DAD.
The DAD principal node and secondary node do not form the cluster. DAD proceeds on the principal node because the secondary node does not affect DAD.