Chapter 21. VXLAN

Virtual eXtensible Local Area Network (VXLAN) is a technology that allows devices to communicate on the same Layer 2 (L2) network, even if they are separated by Layer 3 (L3) boundaries. To overly simplify, it’s like tunneling L2 over L3, but it’s not that easy, because if they made it simple, we wouldn’t have jobs.

Networking people have been taught for decades to cut up L2 broadcast domains as much as possible to limit the potential damage caused by things like broadcast storms. Additionally, as data centers grew in size, we began running up against limits in the switch hardware such as the maximum number of MAC addresses supported. To that end, we have insisted that data centers have their own IP space. I made a lot of money back in the 90s moving companies off of massive bridged environments and moving them to more logical, segmented IP solutions. So why the step backward?

Solutions such as vMotion allow virtual machines (VMs) to be moved from host to host while keeping the machine available for use. That’s a pretty cool thing to do, but to pull it off, the IP address of the VM needs to stay the same. Having data centers in multiple locations is a good thing for disaster avoidance, so those hosts might be in different physical locations. Thus, we have a need for the same IP space to exist in two different physical locations.

Additionally, some clustering technology requires all of the hosts to be within the same IP space. It’s common for companies to want ...

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