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.

VMware gave me early access to NSX hands-on lab a few days prior to VMworld 2013. The lab was meant to demonstrate the basics of NSX, from VXLAN encapsulation to cross-subnet flooding, but I quickly veered off the beaten path and started playing with routing protocols in NSX Edge appliances.

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?

Tore Anderson started his part of the IPv6-Only Data Centers webinar with a comprehensive analysis of numerous design options you have when implementing dual-stack access to your data center.

Unless you decided to live under a rock for the next 20 years or plan to drop out of networking in the very near future, you simply (RFC 2119) MUST watch this video.

A while ago Greg Ferro wrote a great article describing integration of overlay and physical networks in which he wrote that “an overlay network tunnel has no state in the physical network”, triggering an almost-immediate reaction from Marten Terpstra (of RIPE fame, now @ Plexxi) arguing that the network (at least the first ToR switch) knows the MAC and IP address of hypervisor host and thus has at least some state associated with the tunnel.

Marten is correct from a purely scholastic perspective (using his argument, the network keeps some state about TCP sessions as well), but what really matters is how much state is kept, which device keeps it, how it’s created and how often it changes.

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).

In the previous posts I described how a typical overlay virtual networking data plane works and what technologies vendors use to implement the associated control plane that maps VM MAC addresses to transport IP addresses. Now let’s walk through the details of a particular implementation: Nicira Network Virtualization Platform (NVP), part of VMware NSX.

Before Tore Anderson, the rock star behind the IPv6-only data center, started explaining the interesting details of his ideas, I did a short intro explaining the need for IPv4+IPv6 access to your content and the steps you have to take to get there.

You might decide to proceed down the more traditional path (doing 5-6 transitions in the next few years) or deploy IPv6-only data center and be done with it.

A while ago Tomasz Kacprzynski asked me whether I’d ever run RSVP over DMVPN. I hadn’t - after all, you’d only need that in VoIP environments and I try to stay as far away from voice as possible.

In the meantime, Tomasz solved the problem (short summary: you have to turn Phase 3 DMVPN into Phase 2 DMVPN) and wrote a lengthy blog post describing the problem (RSVP split horizon rule) and his solution (including numerous debugging printouts). Definitely worth reading if there’s a non-zero chance you’ll have to get the two working together.