this post was submitted on 06 Jul 2024
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So I guess I must be a leet haxor because of all the businesses I configured for the 172.x space because 192.168.x space was too small and 10.x space was way the hell too big.
wdym too big? That's what subnetting is for.
I know what subnetting is for. That’s why I know which RFC range to use. I’m talking based on the number of devices and needed groupings, 172 is a good sweet spot where 198.x would be a bit tight and 10.x is complete overkill.
Could you please explain, how 172.x is different "size" than 10.x? Don't both of those have 255*255*255 spaces?
Edit: Ok, I made ChatGPT explain it to me. Apparently, with 172.x the convention is to only use range from 172.16.x.x to 172.31.x.x because that range is designated for private networks under some internet regulations...
Yeah. Here’s a breakdown of the allocations and their sizes:
Most home applications only need a single /24 (256 addresses) so they are perfectly fine with 192.168.0.0/24, but as you get larger businesses, you don’t use every single address but instead break it out by function so it’s easier to know what is what and to provide growth in each area.
But tbh, I still don't see why you can't just use 10.x but only as many subnets as you need.
I know jack shit about networking, but I've set up OpenWrt routers a couple of times, and set my home network to 10.99. because that was suggested by a ZeroTier tutorial and I thought that's cool.
You’re technically correct, you can use any of them. It’s honestly just a matter of preference.
For bigger networks, I always went with 10.0.0.0/8 for endpoints, 172.16.0.0/12 for servers and other back-end services, leaving 192.168.0.0/16 for smaller networks like OOB IPMI (eg HP iLO, Dell iDrac) services, cluster heartbeat connections, and certain DMZ segments.
My current work acquired a company with a very poorly provisioned IT department. Their networks all happen to be in the low 192.168.0.0/16 so users VPNing in often end up with wonky IP conflicts. I've heard warnings about similar when selecting subnet ranges, so I just stick with low 192.168.0.0/16 ranges for home networks from which I might potentially VPN into a network I don't control, and I use 172.16.0.0/12 or 10.0.0.0/8 at work as needed and as aligns with our wider topology.
I will also add that I encountered some fun challenges at a small bank I worked at where they clearly under-planned their network and carried a bunch of wonky configs as vestigial networking adaptations as they grew. They did do a cool thing where they made each branch its own /24 subnet so you could tell at a glance exactly what branch someone was connecting from, plus branches could theoretically limp along with an ISP outage, but they didn't the extra steps of setting up edge servers so the end result was a full branch outage during an ISP outage
That’s doable too. A lot of people don’t realize you can route all of those together. It’s even more fun as technically you can route private addresses across public links if you own both ends of the link. Used to see that done at a large ISP to route their internal network and it’d pop new networking admins minds.
ETA: I would use 192.x IPs for unrouted subnets like heartbeats or iSCSI.
Common to see big businesses with multiple locations using P2P VPN binding together all sites like one big LAN. Perhaps not ideal from a security standpoint to have the client network so flat, but eh 🤷
Usually a handful of extra important servers are behind an extra layer of firewall rules and/or on a different VLAN with limits on what devices can connect to them.