Category: virtualization

Every time I mention overlay virtual networking tunnels someone starts worrying about the scalability of this approach along the lines of “In a data center with hundreds of hosts, do I have an impossibly high number of GRE tunnels in the full mesh? Are there scaling limitations to this approach?”

Not surprisingly, some ToR switch vendors abuse this fear to the point where they look downright stupid (but I guess that’s their privilege), so let’s set the record straight.

Answer#1: An overlay virtual networking solution providing logical bridging (aka layer-2 forwarding or switching), logical routing (aka layer-3 switching), distributed or centralized firewalls, load balancers, NAT and VPNs.

Answer#2: A merger of Nicira NVP and VMware vCNS (a product formerly known as vShield).

Oh, and did I mention it’s actually two products, not one?

During the UCS Director Overview Packet Pushers Podcast I listened to recently the participants started discussing the use cases and someone mentioned that UCS Director might not be applicable for small shops with only a few thousand VMs. Let's put that in perspective.

The “What’s coming in Hyper-V Network Virtualization (Windows Server 2012 R2)” blog post got way too long, so I had to split it in two parts: Hyper-V Network Virtualization and the rest of the features (this post).

Multiple overlay network encapsulations are nothing more than a major inconvenience (and religious wars based on individual bit fields close to meaningless) for anyone trying to support more than one overlay virtual networking technology (just ask F5 or Arista).

The key differentiator between scalable and not-so-very-scalable architectures and technologies is the control plane – the mechanism that maps (at the very minimum) remote VM MAC address into a transport network IP address of the target hypervisor (see A Day in a Life of an Overlaid Virtual Packet for more details).

Right after Microsoft’s TechEd event CJ Williams kindly sent me links to videos describing new features in upcoming Windows Server (and Hyper-V) release. I would strongly recommend you watch What’s New in Windows Server 2012 R2 Networking and Deep Dive on Hyper-V Network Virtualization in Windows Server 2012 R2, and here’s a short(er) summary.

This blog post is describing futures that will ship in 2H2013. However, as all the videos mentioned above included live demos, and the preview release shipped on June 24^th, it’s obvious they’re past the “it works so great in PowerPoint” stage.

I explain the intricacies of overlay network forwarding in every overlay-network-related webinar (Cloud Computing Networking, VXLAN deep dive...), but never wrote a blog post about them. Let’s fix that.

First of all, remember that most mainstream overlay network implementations (Cisco Nexus 1000V, VMware vShield, Microsoft Hyper-V) don’t change the intra-hypervisor network behavior: a virtual machine network interface card (VM NIC) is still connected to a layer-2 hypervisor switch. The magic happens between the internal layer-2 switch and the physical (server) NIC.

The original idea behind cloud-as-an-appliance design came from Brad Hedlund’s blog post in which he described how he’d build a greenfield Hadoop or private cloud cluster with servers connected to a Clos fabric. Throw virtual appliances into the mix and you get an extremely simple and versatile architecture:

In his recent blog post Joe Onisick wrote “What network virtualization doesn’t provide, in any form, is a change to the model we use to deploy networks and support applications. [...] All of the same broken or misused methodologies are carried forward. [...] Faithful replication of today’s networking challenges as virtual machines with encapsulation tunnels doesn’t move the bar for deploying applications.”

The long-promised unicast-only VXLAN has finally shipped with the Nexus 1000V release 4.2(1)SV2(2.1) (there must be some logic behind those numbers, but they all look like madness to me). The new Nexus 1000V release brings two significant VXLAN enhancements: unicast-only mode and MAC distribution mode.

I was reading What Network Virtualization Isn’t¹ from Jon Onisick the other day and started experiencing all sorts of unpleasant flashbacks caused by my overly long exposure to networking industry missteps and dead ends touted as the best possible solutions or architectures in the days of their glory:

Meeting Brad Hedlund in person was definitely one of the highlights of my Interop 2013 week. We had an awesome conversation and quickly realized how closely aligned our views of VLANs, overlay networks and virtual appliances are.

Not surprisingly, Brad quickly improved my ideas with a radical proposal: running BGP between the virtual and the physical world.

One of my blogger friends sent me an interesting observation:

After talking to networking vendors I'm inclined to think they are going to focus on a mesh of overlays from the TOR, with possible use of overlays between vswitch and TOR too if desired - drawing analogies to MPLS with ToR a PE and vSwitch a CE. Aside from selling more hardware for this, I'm not drawn towards a solution like this bc it doesn't help with full network virtualization and a network abstraction for VMs.

The whole situation reminds me of the good old SNA and APPN days with networking vendors playing the IBM part of the comedy.

Brad Hedlund wrote another great article, this one explaining the fundamentals of network virtualization. As you'll see, VMware (and everyone else) aims way higher than replacing VLANs with overlay networks. Highly recommended!

Regardless of what the vendors are telling you, it’s hard to get data center disaster recovery right (unless you’re running regular fire drills), and your job usually gets harder due to the intricate (sometimes undocumented) intertwining of physical and virtual worlds. For example, do you know how to get the firewall and load balancer configurations from the failed site implemented in the equipment currently used at disaster recovery site?

Imagine a simple application stack with a few web servers, app servers and two database servers. There’s a firewall in front of the web servers and a load balancer tying all the segments together.