Juniper Switch Software Install, Upgrade, or Downgrade using USB port

I bought 2 EX4200 from eBay and wanted to do virtual-chassis.  Here are some things I learned:

1. The 2 switches came with different Software version 10 and 12.

2. Had to buy the vcp cable for virtual chassis.

3. Had to connect the cable in the back vcp-0 to vcp-0 and vcp-1 to vcp-1 to make a ring, else wouldn't work.  You'll see a status of "NotPrsnt."

4. Both switches need to be on the same software, so this is what I did:

I had to downgrade the new switch to 10.4R5.5 – the simplest and safest way to do this is with the switch in standalone and put the image on a USB Key and plug in back of EX4200.

Here are the steps:

a. Download your image from Juniper.net and put in the root of a FAT32 formatted USB Key in your laptop/

b. Insert the USB key into the back of the EX4200 and boot the switch if Needed.
Then mount the usb key

root@:RE:0% mount_msdosfs /dev/da1s1 /mnt

Once the USB has been mounted you can run the request system software add command. This command installs any software version you specified...upgrade or downgrade.

root> request system software add  /mnt/jinstall-ex-4200-10.4R5.5-domestic-signed.tgz

You now have to be patient as this process takes a few minutes, once the image has been loaded you will be asked to reboot.

Checking pending install on fpc0
Validating on fpc0
Done with validate on all virtual chassis members
fpc0:
WARNING: A reboot is required to install the software
WARNING:     Use the ‘request system reboot’ command immediately

root@:RE:0% cli

{master:0}

root> request system reboot 

Reboot the system ? [yes,no] (no) yes
*** FINAL System shutdown message from root@ ***                            
System going down IMMEDIATELY

Once the switch has rebooted a show version will show the switch is now running the 10 or any Image you had installed.

root> show version