Category: Data Center

Almost everyone agrees the current way of implementing virtual networks with dumb hypervisor switches and top-of-rack kludges (including Edge Virtual Bridging – EVB or 802.1Qbg – and 802.1BR) doesn’t scale. Most people working in the field (with the notable exception of some hardware vendors busy protecting their turfs in the NVO3 IETF working group) also agree virtual networks running as applications on top of IP fabric are the only reasonable way to go ... but that’s all they currently agree upon.

Very short answer: no.

You might think that layer-3 switches perform bridging and routing, while routers do only routing. That hasn’t been the case at least since Cisco introduced Integrated Routing and Bridging in IOS release 11.2 more than 15 years ago. However, Simon Gordon raised an interesting point in a tweet: “I thought IP L3 switching includes switching within subnet based on IP address, routing is between subnets only.”

Layer-3 switches and routers definitely have to perform some intra-subnet layer-3 functions, but they’re usually not performing any intra-subnet L3 forwarding.

Yesterday I got pulled into a layer-2 DCI tweetfest. Not surprisingly, there were profound opinions all over the place, including “We've been doing it (OTV) for almost a year now. No problems.”

OTV is in fact the least horrible option – it does quite a few things right, including tight control of unicast flooding and reduction of STP scope.

Today I stumbled across this gem in the acmqueue blogs:

You might as well ask why people insist on not wearing seatbelts after all of the years that particular technology has been proven to save lives.

A while ago, a tweet praising the wonders of 802.1BR piqued my curiosity. I couldn’t resist downloading the latest draft and spending a few hours trying to decipher IEEE language (as far as the IEEE drafts go, 802.1BR is highly readable) ... and it was déjà vu all over again.

Short summary: 802.1BR is repackaged and enhanced 802.1Qbh (or the standardized version of VM-FEX). There’s nothing fundamentally new that would have excited me.

I often get three questions about TRILL: Are the TRILL standards finalized? Has anyone implemented it? Is it useful?

Short answers: Yes, No, Maybe (although I remain unconvinced).

Almost a year ago, I predicted that eventually the hypervisor vendors will wake up and realize it’s time to get rid of VLANs and decouple virtual networks from the physical world. We’ve got the first glimpse of the brave new world a few weeks after that post was published with the VXLAN launch, but that was still a Cisco’s solution running on top of VMware’s (and now everyone else’s) hypervisor. The recent VMware’s acquisition of Nicira proves that VMware finally woke up big time.

Every time I rant about large-scale bridging and stretched L2 subnets, someone inevitably points out that Carrier (or Metro) Ethernet works perfectly fine using the same technologies and principles.

I won’t spend any time on the “perfectly fine” part, but focus on the fundamental difference between the two: the use case.

Sometime in 2012, Chuck Hollis described how some of EMC customers use long-distance workload mobility. Not surprisingly, he focused on the VPLEX Metro part of the solution and didn’t even mention the earth-flattening requirements this idea imposes on the network. I guess you already know my views on that topic, but regardless of my personal opinions, he got me curious.

David Le Goff sent me several great SDN-related questions. Here’s the first one:

What is your take on the performance issue with software-based equipment when dealing with general purpose CPU only? Do you see this challenge as a hard stop to SDN business?

Short answer (as always) is it depends. However, I think most people approach this issue the wrong way.

This post is probably a bit premature, but I’m positive your CIO will get a visit from a vendor offering clean-slate OpenFlow/SDN-based data center fabrics in not so distant future. At that moment, one of the first questions you should ask is “how well does your new wonderland integrate with my existing network?” or more specifically “which L2 and L3 protocols do you support?”