F5 is taking more than 50 mins to reboot

You cannot downgrade from v12 to v11. When upgrading, you must ensure one partition remains with old version as a fallback option.

Did you click "install configuration" when rebooting to v11 from v12? If yes, your best bet is to do a clean install of v11, and manually migrate your configuration back to v11. On your v12 boot location, look for your configuration elements in

/config

So can you help me what should i do to make box up

Your configuration probably did not install and it may have reverted to default management IP address. If it's a physical appliance, you may be able to access it with AOM (Always On Management) IP address. If that's not setup or if the box does not support AOM, you're out of luck here.

Do you have a contact with someone who is present at the data center? Either boot it back to v12 partition, or ask him to use the front panel to configure management IP to what it should be (he can also confirm if this has changed)

Chances are your configuration move from 11 to 12 has a few lines of code in the BIGIP configuration the new version doesn't like. It is stuck in a reboot loop.

If you have terminal access run the following

It will show you an error like such ...

0107146f:3: Self-device state mirroring address cannot reference the non-existent Self IP (101.10.xx.xx); Create it in the /Common folder first. Unexpected Error: Loading configuration process failed

If this is similar to the error do the following

once in vi press '/' perform a search on the IP listed as the self ip that causes error comment out the IP address (two sections in this case)

:X to save out of VI

Should load successfully once all invalid IP addresses are removed, in the event it does not it will present another IP address in error, in this event comment out the other IP address and reload the configuration once again

once the configuration is loaded run the following

This will reboot into the volume.