I'd like to downgrade VDX6740 from 5.0.1 to 4.1.3 to add them into the fabric, is there a procedure

[P-Didi]

The new switches to add in the fabric are running newer versions (5.0.1) than the one on the fabric (4.1.3), so I'd need to downgrade. When trying, first told me to disable ag. Did so and reboot occured. when trying now get this messag;

VDX6740# firmware download usb directory nos4.1.3
Performing system sanity check...

ISSU is not supported to the target firmware version. Please specify the manual or coldboot option in the command-line for download.
The preinstall script failed.

Is there a manual on how to do this ?

PS: this is urgent as I have to connect them tonight...

Thanks.

Best regards,

Didier.

[doc]

Since you are running in VF (fabric) mode, and you wish to downgrade the firmware, you cannot use the ISSU process(In Service Software Upgrade) when in VF mode. Brocade wants to protect the configuration of the fabric as running, and some of the features introduced in the 5.0.x version of NOS are not supported in 4.1.x version. Therefore - you must do a more manual, and intrusive download in order to get the firmware you need. Perform the download of the firmware with the manual option, or use coldboot via the command line to get the firmware on the switch. NOTE; this is disruptive to traffic when the switch is rebooted.

Alternately, you can disable VF on all nodes by getting rid of any service or transport VFs configured. Then in global configuration mode run: no vcs virtual-fabric enable. Then you can use the ISSU method to downgrade the firmware as needed.  NOTE; this is disruptive to traffic when the switch reboots.

Don't forget to save your running config and startup config  off switch for safety, and insure the running and startup config scripts are as you want them prior to making firmware changes.

Best of luck

doc