What gets interesting with QFabric is the migration path to and from QFabric, and how QFabric can fit into the data center. In a fit of whiteboard craziness, we mapped out some scenarios. A couple of things come clear:
- To the rest of the network, QFabric is just a L2/L3 switch. It's one bridge in a spanning tree, and outside QFabric, it's just Ethernet. That means you can plug a QFfabric into the rest of your network and it will be loop-free.
- All the rest of your L2/L3 network will behave just fine, and you can run any other network equipment, like a Cisco Nexus side-by-side.
- Any requirements such as reaching hosts defined by routes on an external router or passing traffic through a load balancer mean traffic many have to pass out and back in to QFabric.
If you have already invested in Juniper's QF 3500s, the EX line is not supported and you want to migrate to QFabric, you need a QFInterconnect and a QFDirector, although Juniper recommends pairs for redundancy. You can cable to your existing QF 3500s and they become part of the Qfabric. Take them out of the QFabric, and they become l2/L3 switches. Pretty nice investment protection.
I like it. QFabric is a fairly simple design—simple is good. No need to worry about mutlipath Ethernet protocols like TRILL, SPB, LAG or MLAG. It only scales to 6,144 10-Gbit ports with over subscription, 2,048 if you want non-blocking (that's 16 10-Gbit ports per QFNode). If you dual-home your servers, that only 3,072 servers. I say only tongue in cheek. That's a lot of servers for most organizations, and I will go out on a limb and assume that if you're looking at that kind of scale, it's either a special-purpose computing center or a hosting or cloud provider.
The other elephant in the room is cost. That's a topic I will take up later, as well as digging a little deeper into the design scaling issues. Of course, there are a number of other things to consider, like distance limitations of the OM-4 cable, cable layout and designing the L2/L3 network within QFabric. But if you are looking at upgrading from a 1-Gbit to a 10-Gbit network and you want to take advantage of the new features that network fabrics such as Brocade's VCS, Cisco's Fabricpath and Juniper's QFabric offer, it's worth a long hard look. And I bet the proprietary features will be less important the deeper you look.
Disclosure. I traveled to Sunnyvale on my company's dime. Juniper fed me a hamburger, chips and a soda, and gave me a pen.
