Network Stacks

A network stack is the software that lets a host communicate with the network. A host can run with an IPv4-only network stack, an IPv6-only network stack, or a dual-stacked setup.

You’re already familiar with an IPv4-only stack—it’s what most hosts ran for much of the past 30 years. An IPv4-only stack can communicate only over IPv4. Today, an IPv4-only stack gets you access to the entire Internet, with a few deliberate exceptions. That will not be true in a few years.

Likewise, an IPv6-only stack can communicate with only IPv6 hosts. Because most Internet sites don’t yet support IPv6, running an IPv6-only stack isn’t practical at this point. It is, however, an excellent way to test your IPv6 infrastructure and connectivity.

The most common configuration these days is a dual-stack setup. Client hosts try to use both IPv4 and IPv6, preferring one over the other. I recommend configuring hosts with dual stacks, preferring the stack with better connectivity. (If you get IPv6 connectivity through a tunnel, it’s not as fast as your IPv4 connectivity.) If you have equal IPv4 and IPv6 connectivity, use whichever you prefer. IPv6 works well enough that I often don’t realize that I’m using it until I analyze my traffic.

You don’t need to do anything special to enable IPv6 on OpenBSD—an IPv6 address, a default router, and a DNS server, and away you go.