You wouldn’t believe what your second most pressing problem is when you lose electricity for a few days in the middle of a winter storm: freezer. Being a good engineer focused on redundant solutions, I bought a diesel generator before moving into the hills to keep the freezer at a reasonably low temperature in case of a long-term power loss.

I also thought about using the same generator to run our central heating. As always, I found a huge disconnect between theory and practice.

Every time I plug a new device into my Windows laptop and it automatically discovers the device type, installs the driver, configures the devices, and tells me it’s ready for use, I wonder why we can’t have get the same level of automation in networking.

Consider, for example, a well-known vSphere link failover issue: if you forget to enable portfast on server-facing switch ports, some VMs lose connectivity for up to 30 seconds every time a switch reloads.

You probably know the three steps to a disaster recovery plan: Disaster. Recovery. Plan. It’s amazing how true that joke is, and how unprepared we tend to be for infrequent outages.

This is totally out of context, but imagine the consultants and marketers promising us unicorn-generated nirvana like follow-the-sun VM mobility or large-scale flow-based forwarding encountering Alice.

Source: dilbert.com

The layer-3-only Hyper-V Network Virtualization forwarding model implemented in Windows Server 2012 R2 thoroughly confuses engineers used to deal with traditional layer-2 subnets connected via layer-3 switches.

As always, it helps to take a few steps back, focus on the principles, and the “unexpected” behavior becomes crystal clear.

2014-02-05: HNV routing details updated based on feedback from Praveen Balasubramanian. Thank you!

If you want to implement overlay virtual networking with VMware products today, you have two options: use vCNS 5.5 or NSX for vSphere… and I would be hard pressed to choose one or the other.

When I started blogging in 2006, I had no idea that I’d still be doing it 8 years later… and I never dreamed of writing my 2000th post (this one, according to my blogging platform).

A virtual cake I got from my lovely daughter ;)

From the IPv6 Trivia department: can a host with an ULA address reach a service with a global IPv6 address? Can a host with only a link-local address reach a service with a global IPv6 address? The answer to both questions might be Yes (but you better know what scopes and zones are if you want to figure it out).

Just in case you've missed it: the ultimate explanation of DevOps, NetOps and other automation ideas.

Source: xkcd.com

You know how hard it is to get the network traffic statistics: interface counters are too coarse, Netflow records are too granular, Sflow is sampling… life is hard for network monitoring Goldilocks.

In the Network Monitoring video (part of Real-Life OpenFlow Use Cases webinar) I explained an interesting alternative: you could get (hardware permitting) traffic counters with ever OpenFlow flow entry, resulting in any granularity you need.

Having “do we need ULA” blogologs with Ed Horley is great … and the best part of them is that we’re both right (aka: It Depends). OK, let’s try to quantify that last part.

Almost three years ago the OpenFlow/SDN hype exploded and the Open Networking Foundation started promoting the concept of physically separate control and data planes. Let’s see how far its founding members got in the meantime:

Chris Wahl claimed in one of his recent blog posts that vSphere doesn't need LAG band-aids. He's absolutely right – vSphere’s loop prevention logic alleviates the need for STP-blocked links, allowing you to use full server uplink bandwidth without the complexity of link aggregation. Now let’s consider the networking perspective.

More news from the IPv6 is not like IPv4 department: there's no DF bit in IPv6, so you have to use slightly different troubleshooting tricks to figure out the path MTU size (and they depend on the operating system). More in a detailed blog post by my good friend Matjaž Straus.

The first part of the Real-life OpenFlow Use Cases webinar focused on controller design and implementation choices that can significantly impact the scalability of an OpenFlow solution:

• Proactive versus reactive flow setup;
• Hop-by-hop versus path-based forwarding;
• State explosion with OpenFlow 1.0;

You could tell we had great fun with these topics: we spent more than half an hour on five slides.