Category: LAN

QFabric from Juniper is probably the best data center fabric architecture (not implementation) I’ve seen so far – single management plane, implemented in redundant controllers, and distributed control plane. The “only” problem it had was that it was way too big for data centers that most of us are building (how many times do you need 6000 10GE ports?). Juniper just solved that problem with a scaled-down version of QFabric, officially named QFX3000-M.

VMware has a fantastic-looking cloud provisioning tool – vCloud director. It allows cloud tenants to deploy their VMs and create new virtual networks with a click of a mouse (the underlying network has to provide a range of VLANs, or you could use VXLAN or vCDNI to implement the virtual segments).

Needless to say, when engineers not familiar with the networking intricacies create point-and-click application stacks without firewalls and load balancers, you get some interesting designs.

Michael sent me an interesting question:

I work in a rather large enterprise facing a campus network redesign. I am in favor of using a routed access for floor LANs, and make Ethernet segments rather small (L3 switching on access devices). My colleagues seem to like L2 switching to VSS (distribution layer for the floor LANs). OSPF is in use currently in the backbone as the sole routing protocol. So basically I need some additional pros and cons for VSS vs Routed Access. :-)

The follow-up questions confirmed he has L3-capable switches in the access layer connected with redundant links to a pair of Cat6500s:

Like every other blogger, I get occasional e-mails from people fishing for free consulting or second opinion (note: asking a serious technical question is a totally different story; as many people know, I always try to reply and help) and as I’m totally overloaded with OpenFlow symposium and Net Field Day these days, I decided to share one of the better ones.

Chris Marget sent me the following interesting observation:

One of the things we learned back at the beginning of Ethernet is no longer true: hardware filtering of incoming Ethernet frames by the NICs in Ethernet hosts is gone. VMware runs its NICs in promiscuous mode. The fact that this Networking 101 level detail is no longer true kind of blows my mind.

So what exactly is going on and does it matter?

You probably know the old saying – if the mountain doesn’t want to come to you, you have to go out there and climb it. vCider, a brand-new startup launching their product at Gigaom Structure Launchpad, decided to do something similar in the server virtualization (Infrastructure-as-a-Service; IaaS) space – its software allows IaaS customers to build their own virtual layer-2 networks (let’s call then vSubnets) on top of IaaS provider’s IP infrastructure; you can even build a vSubnets between VMs running within your enterprise network (private cloud in the cloudy lingo) and those running within Amazon EC2 or Rackspace.

Full disclosure: Chris Marino from vCider got in touch with me in early June. I found the idea interesting, he helped me understand their product (even offered a test run, but I chose to trust the technical information available on their web site and passed to me in e-mails and phone calls), and I decided to write about it. That’s it.

I was listening to the HP Virtual Connect (VC) PPP podcast recently and got the impression that HP VC is a weirdly convoluted product. I started wondering what exactly they were thinking when they were designing it ... and had the epiphany when Ken Henault took a step back and explained the history leading to the current complexity (listen to the Packet Pushers podcast to get the whole story)

A few months ago VMware decided to kick away one of the more stubborn obstacles in their way to Data Center domination: the networking team. Their vCloud architecture implements VLANs, NAT, firewalls and a bit of IP routing within the VMware hypervisor and add-on modules ... and just to make sure the networking team has no chance of interfering, they implemented MAC-in-MAC encapsulation, making their cloudy dreamworld totally invisible to the lowly net admins.

The Internet Exchange and Peering Points Packet Pushers Podcast is as good as the rest of them (listen to it first and then continue reading), but also strangely relevant to the data center engineers. When you look beyond the peering policies, route servers and BGP tidbits, an internet exchange is a high-performance large-scale layer-2 network that some data center switching vendors are dreaming about ... the only difference being that the internet exchanges have to perform extremely well using existing products and technologies, not the shortest-path-bridging futures promised by the vendors.

It looks like everyone (and their dog) is writing about DCB and FCoE these days, but occasionally we get a fresh thought: Ron Fuller compares FC/Ethernet to East/West coast mentality. Great analogy ;)

Recently I’ve stumbled across a year-old post by James Ventre describing the reasons output rate on an Ethernet-type interface (as reported by the router) never reaches the actual interface speed. One of them: inter-frame/packet gap (IPG).

I was stunned ... I remember very well the early days of thick/thin coax Ethernet when the IPG was needed for proper carrier sense/collision avoidance detection (probability of a collision decreases drastically as you introduce IPG), but on a high-speed point-to-point full duplex link? You must be kidding.

Ethan Banks has a great article @ PACKETattack: in Assembly Required – Interconnecting 2 Ethernet Chassis Switches he describes various options you have when you want to connect your redundant core switches. Using more than one physical link is the obvious choice; most people are careful enough to use at least two linecards, but the true magic begins when you start considering the bandwidth allocation to individual linecards and port groups within linecards.

Tired of losing half of your bandwidth to spanning tree? TRILL will solve all your problems, bring the world peace and make better coffee than Starbucks (hint: the second claim is fake and the third one is not so hard to achieve).

Undoubtedly TRILL is an interesting technology that can alleviate the spanning tree limitations. Unfortunately I’ve seen a very similar technology being heavily misused in the past (resulting in some fantastic failures) and remain skeptical about the deployment of TRILL. My worst case scenario: TRILL will make it too simple to deploy plug-and-pray bridged (vendors will call them “switched”) networks with no underlying design that will grow beyond control and implode.

Greg Ferro has kindly invited me to be a guest author on his excellent blog Etherealmind.com and I simply had to spill my thoughts on TRILL in the TRILL: It’s a DéJà-Vu All Over Again article after they’ve been discussing it during one of the Packet Pushers podcast.

Ever since I’ve figured out how to explain complex topics to bright engineers, I wanted to develop content (books, courses, documents) that explained (in this order):

• The Big Picture and WIIFM (What will the student gain by understanding and deploying something based on what I’m describing).
• How the technology we’re using actually works (remember: knowledge, not recipes) and finally
• How to configure, monitor and troubleshoot the actual boxes used to build the solution.

I’m positive you agree this approach makes perfect sense, and every now and then I’ve managed to get it right (for example, in the MPLS VPN books). Unfortunately, you’re often facing an uphill battle, as people want to focus on hands-on topics and hate to learn why things work the way they do instead of memorizing recipes like “Thou shalt not have more than 3 OSPF areas per router”.

Unveiling of the Cisco IOS release 15.1(1)T was the extreme opposite of the CRS-3 and Catalyst 3750-X splashes; the next release of one of the foundations of Cisco’s core business deserved a modest two-paragraph mention in the What's New in Cisco Product Documentation page.

If you’re a voice guru, you’ll probably enjoy the list of 20+ voice-related new features, including the all-important Enhanced Music on Hold. For the rest of us, here’s what I found particularly interesting: