Comment 5 for bug 1629133

Ideally, all address blocks used by DevStack (including via plugins) should inherit a common v4 /16 prefix which is set by a _single_ configuration option. Subnets of that /16 ought to then be registered with a data structure early in setup and DevStack should fail out with a comprehensible error message as soon as it spots a conflict/overlap between any of these subnets (bonus points for checking whether they also overlap any preexisting local nets for the system). This would not only make it less likely to cause spontaneous conflicts due to picking excessively-sized address ranges from all over RFC 1918 space, but would also make the network configuration trivially portable (such that we could even signal DevStack on a provider-by-provider basis in our jobs as to a base prefix we've deemed safe in that particular environment).

As for asking an RIR for a (fairly large) offline v4 test allocation on the grounds that avoiding conflicts with RFC 1918 space is "hard," I have serious doubts you'll convince them. I've had a hard enough time over the years justifying _legitimate_ connected uses for new v4 allocations. This is something that can be solved in software, it just needs some thought and planning.