What's not to like about virtualization? It's green, it saves rack space, it even eases remote access issues. Well, one thing virtualization doesn't do is make troubleshooting easy! For example: If you have an application server, a middleware server, and a SQL server all talking over the virtual network, how in the world can you get a glimpse into their conversations? It's not like you can slap a tap on the gig port and fire up a protocol analyzer, because the virtual network never pokes its head into the physical world.

I and other members of the Interop NOC team ran into this exact issue when Neal Allen of Fluke Networks started looking at logical places to install network troubleshooting gear during Hot Stage for Interop Las Vegas 2009. He was carrying a bunch of Net Optics taps and suddenly stopped dead in his tracks, a quizzical look on his face. He then started asking around: Just how do you tap the virtual network under VMware? What happens if we have problems between servers that only talk over the virtual network? If you slap a full analyzer into a virtual machine, have you now changed the environment by sucking up a bunch of resources to observe the virtual network?

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As I dug deeper into these questions, I remembered a conversation with a friend about the migration of his SaaS application from an internal datacenter to Amazon EC2/S3. He gave me this advice: If your application is well developed and no longer in the troubleshooting stage, clouds can be wonderful. But the cloud isn't a friendly place for troubleshooting. Trying to track down bugs in the growing cloud-based system was costing him oodles of time and money.

So just how do you get a look inside your virtual network? I stumbled across the answer during an update session by Network Instruments on the Observer product line: virtual taps. If you set a VMware virtual switch (vSwitch) and virtual network adapter (vNIC) to promiscuous mode, the vNIC will receive all traffic that flows through the vSwitch. Network Instruments' virtual tap, called vTaps, is software that installs inside a VMware virtual machine, collects all of this vSwitch traffic, and directs it to a physical NIC and into a Network Instruments probe.