I had an interesting discussion on Facebook a few weeks ago with another network engineer, which went something like this:
I'd like to smack the person who thought it would be a good idea to put a network of 200+ devices onto a subnet of 192.168.2.0/23 (no, that ending 3 is not a typo), as well as (quite possibly) the same person who thought it would be a good idea to install a headless firewall onto hardware without VGA or Console [or serial] output.
I don't get it. If I'm creating a network for 200+ devices and I want them to all be on the same broadcast domain, /23 is the ticket bud with 510 useable. Is it the fact there is no network segmentation that bothers you?
Creating a 10/16 would have been a much better way to go (in terms of making it clean and easy to deal with later down the road). Plus, this particular client is growing like mad and should have 500+ devices by next year.
I would avoid anything over /22 for a broadcast domain unless you had a really good reason. What kind of switching and routing you got? Sounds like its time for an SVI or a router on a stick.
Basically, my annoyance was that whoever setup the original network did so with a 192.168.2.0/23, causing the 192 network to be slit into 2 separate IP blocks (I didn't like the fact that the ending octet was different, but the same subnet).
So here's my question:
Is there a network performance concern to setting up networks with a lower subnet mask than is actually required by the number of devices on the network? Are there any other reasons why this is a bad idea (Aside from the security & logical reasons of creating smaller subnets - creating certain VLANs, separating 1 part of the network from the other, etc....)?
As an aside, I skimmed through top answer to the Canonical Question on IPv4 Subnetting, and learned a few things, but it didn't directly answer my question from a performance point of view. Specifically, though, I found the "Top three main reasons why you would subnet a network" section towards the end of that answer helpful.
In my mind, if I were to put a total of 30 devices onto a 10/16 subnet, there wouldn't be a problem. However, if I were to put 2048 devices, or so, onto a 10/16 without any routers in between or layer 3 switching, then obviously there would be a problem, with a lot of devices trying to broadcast.