Typically a network interface has an IP address (hopefully an IPv6 address too), but sometimes there's a need to bring up an interface without one. Turns out there is a standard way to set this up on Redhat-like system.

In /etc/sysconfig/networking-scripts/ifcfg-ethX, set:

BOOTPROTO="none"
ONBOOT="yes"

And that's it. Easy peasy.