One of the outstanding features of the EX-series switches that Juniper offers is the ability to mix and match hardware types into a Virtual Chassis (VC). The virtual chassis technology allows you to cluster up to ten EX4200-series switches for high availability and easier management. Communication between the switches in the VC is at an impressive 128 Gbps. The individual member switches in a VC can be any model of EX4200 with any mix of supported power supply units, Power over Ethernet options, and uplink modules. Management is simplified via a single management interface, a common JUNOS software version, one single configuration file, and the ability to add new members quickly and easily. You can even have VC members in separate locations of your network to create a more unified and highly redundant network.
Before diving into the complexities of the VC protocols, topologies and troubleshooting, I wanted to start off with a situation I ran into that may be useful as you build your Juniper network and take advantage of the VC technology. Lets say you have a stack of EX4200′s in a working VC topology and you want to power down the stack and just turn on one member of the VC for testing or because you are moving the stack, etc. Here is what you might find. When you power on one of the switches in a VC without the entire set of switches in the VC being turned on everything will appear normal on the switch. The lights are on and the end point says “connected”. But you cannot access anything. So what’s going on? Well, if you were to connect to this switch via a console cable and issue the command ‘show virtual-chassis status‘, you would see your switch reporting “Not Prsnt”. In order to fix this, just go into configure mode and type ‘request virtual-chassis restart‘. This will allow you to use this switch outside of the VC. While there may be other ways to do this, this is the method that worked for me and the one recommended by J-TAC. Once you are ready to put the switch back into the VC, just add it back into the stack and turn on all of the members and everything should work as it did before.
Stay tuned for more information on VC technology as I would like to continue discussing it and exploring it.
