[e12e]

For benchmarking loopback connections, addressing really shouldn't be an issue, as you have an entire /8-subnet to split between your client(s) and server(s) (127.0.0.0/8). You would need some logic to set up eg 10.000 listening servers, and 1000.000 clients to get it working, and at some point you'd probably run into memory or other limits.

I'm a little surprised some simple googling didn't turn up any examples of this - I'm sure someone have tried it out in order to do some benchmarking of high-performance network servers/services?

Apparently ipv6 changes this to a single (loopback) address, but then again, with ipv6 you can use entire subnets per network card.