Category: virtualization

It’s hard for me to admit, but there just might be a corner use case for split subnets and inter-DC bridging: even if you move a cold VM between data centers in a controlled disaster avoidance process (moving live VMs rarely makes sense), you might not be able to change its IP address due to hard-coded IP addresses, be it in application code or configuration files.

Disaster recovery is a different beast: if you’ve lost the primary DC, it doesn’t hurt if you instantiate the same subnet in the backup DC.

Brad Hedlund wrote a thought-provoking article a few weeks ago, claiming that the horseshoes (or trombones) and spaghetti created by virtual workloads and appliances deployed anywhere in the network don’t matter much with new data center designs that behave like distributed switches. In theory, he’s right. In practice, less so.

After I published the Decouple virtual networking from the physical world article, @paulgear1 sent me a very valid tweet: “You seemed a little short on suggestions about the path forward. What should customers do right now?” Apart from the obvious “it depends”, these are the typical use cases (as I understand them today – please feel free to correct me).

A few days ago I had the privilege of being part of an VXLAN-related tweetfest with @bradhedlund, @scott_lowe, @cloudtoad, @JuanLage, @trumanboyes (and probably a few others) and decided to write a blog post explaining the problems VXLAN faces due to lack of control plane, how it uses IP multicast to solve that shortcoming, and how OpenFlow could be used in an alternate architecture to solve those same problems.

Isn’t it amazing that we can build the Internet, run the same web-based application on thousands of servers, give millions of people access to cloud services … and stumble badly every time we’re designing virtual networks. No surprise, by trying to keep vSwitches simple (and their R&D and support costs low), the virtualization vendors violate one of the basic scalability principles: complexity belongs to the network edge.

In the VMware vSwitch – the baseline of simplicity post I described simple layer-2 switches offered by most hypervisor vendors and the scalability challenges you face when trying to build large-scale solutions with them. You can solve at least one of the scalability issues: VM-aware networking solutions available from most data center networking vendors dynamically adjust the list of VLANs on server-to-switch links.

If you’re looking for a simple virtual switch, look no further than VMware’s venerable vSwitch. It runs very few control protocols (just CDP or LLDP, no STP or LACP), has no dynamic MAC learning, and only a few knobs and moving parts – ideal for simple deployments. Of course you have to pay for all that ease-of-use: designing a scalable vSwitch-based solution is tough (but then it all depends on what kind of environment you’re building).

Dan sent me an interesting comment after watching my Data Center 3.0 webinar:

I have a different view regarding VMware vSwitch. For me its the best thing happened in my network in years. The vSwitch is so simple, and its so hard to break something in it, that I let the server team to do what ever they want (with one small rule, only one vNIC per guest). I never have to configure a server port again :).

As always, the right answer is “it depends” – what kind of vSwitch you need depends primarily on your requirements.

I stumbled upon VMsafe Network API (the API formerly known as dvFilter) while developing my VMware Networking Deep Dive webinar, set up the vShield App 4.1 in a lab, figured out how it works (including a few caveats), and assumed that’s how most virtual firewalls using dvFilter work. Boy was I wrong!

An engineer attending my VMware Networking Deep Dive webinar has asked me a tough question that I was unable to answer:

What happens if a VM running within a vSphere host sends a BPDU? Will it get dropped by the vSwitch or will it be sent to the physical switch (potentially triggering BPDU guard)?

I got the answer from visibly harassed Kurt (@networkjanitor) Bales during the Networking Tech Field Day; one of his customers has managed to do just that.

Update 2011-11-04: The post was rewritten based on extensive feedback from Cisco, VMware and numerous readers.

Yesterday New York Times published an article covering Nicira, a semi-stealthy startup working on an open source soft switch (Open vSwitch) and associated OpenFlow-based controller, triggering immediate responses from GigaOm and Twilight in the Valley of the Nerds. While everyone got entangled in the buzzwords (or lack of them), not a single article answered the question “what is Nicira really doing?” Let’s fix that.

Got this set of questions from a CCIE pondering emerging technologies that could be of potential use in his data center:

I don’t think OpenFlow is clearly defined yet. Is it a protocol? A model for Control plane – Forwarding plane FP interaction? An abstraction of the forwarding-plane? An automation technology? Is it a virtualization technology? I don’t think there is consensus on these things yet.

OpenFlow is very well defined. It’s a control plane (controller) – data plane (switch) protocol that allows control plane to:

Every time I’m discussing the VXLAN technology with a fellow networking engineer, I inevitably get the question “how will I connect this to the outside world?” Let’s assume you want to build pretty typical 3-tier application architecture (next diagram) using VXLAN-based virtual subnets and you already have firewalls and load balancers – can you use them?

The product information in this blog post is outdated - Arista, Brocade, Cisco, Dell, F5, HP and Juniper are all shipping hardware VXLAN gateways (this post has more up-to-date information). The concepts explained in the following text are still valid; however, I would encourage you to read other VXLAN-related posts on this web site or watch the VXLAN webinar to get a more recent picture.

I’ve first heard about CloudSwitch when writing about vCider. It seemed like an interesting idea and I wanted to explore the networking aspects of cloud VLAN extension for my EuroNOG presentation. My usual approach (read the documentation) failed – the documentation is not available on their web site – but I got something better: a briefing from Damon Miller, their Director of Technical Field Operations. So, this is how I understood CloudSwitch works (did I get it wrong? Write a comment!):

Just a few hours after VXLAN was launched, I received an e-mail from one of my readers asking (literally) if VXLAN was awesome or braindead. I decided to answer this question (you know the right answer is it depends) and a few others in a FastPacket blog post published by SearchNetworking.

I wrote the post before NVGRE was published and missed the “brilliant” idea of using GRE key as virtual segment ID.

Read more @ SearchNetworking