How Many IPs in a /30 Subnet?
If you've ever configured a router, set up a VPN, or dealt with anything network-related, you've probably encountered the term "/30" and wondered what it actually means. And that's it. The short answer? A /30 subnet contains 4 total IP addresses, but only 2 are usable for devices. Two addresses you can actually assign to computers, routers, or servers Most people skip this — try not to..
But here's where it gets interesting — most people assume they need more addresses than they actually do. Understanding exactly what a /30 gives you (and what it doesn't) can save you from wasting IP space or, worse, running out of addresses when you thought you had plenty Still holds up..
What Is a /30 Subnet, Exactly?
Let's break it down. The "/30" comes from CIDR notation — Classless Inter-Domain Routing, which is just a fancy way of saying "how many bits in the subnet mask are set to 1."
A /30 means 30 out of 32 bits are used for the network portion. That leaves exactly 2 bits for host addresses. Here's the math:
- Total addresses in a /30: 2^2 = 4
- Usable addresses: 4 - 2 = 2
Those other two addresses? Now, one is the network address (the first IP in the block), and one is the broadcast address (the last IP). They're reserved and can't be assigned to devices That's the part that actually makes a difference..
Here's one way to look at it: if you have the subnet 192.168.1.0/30:
- 192.168.1.0 — network address (reserved)
- 192.168.1.1 — first usable IP
- 192.168.1.2 — second usable IP
- 192.168.1.3 — broadcast address (reserved)
How /30 Compares to Other Subnet Sizes
It helps to see /30 in context. Here's a quick look at common subnet sizes:
| Subnet | Total IPs | Usable IPs |
|---|---|---|
| /30 | 4 | 2 |
| /29 | 8 | 6 |
| /28 | 16 | 14 |
| /27 | 32 | 30 |
| /24 | 256 | 254 |
You can see the pattern — each additional bit doubles the available addresses. But the two reserved addresses always stay the same, which is why a /30 feels so tight. You're literally getting the bare minimum for two devices to talk to each other Worth keeping that in mind. Which is the point..
Why Does a /30 Matter?
Here's the thing — /30 is one of the most commonly used subnet sizes in production networking, even though it seems tiny. Now, why? Because it's perfect for point-to-point connections The details matter here..
Think about a connection between two routers. You need exactly two — one for each router's interface. You don't need 254 addresses. You don't need 14 addresses. A /30 gives you exactly that, with no waste Not complicated — just consistent. Worth knowing..
Real-world examples where /30 is the standard:
- WAN links — connections between routers at different sites
- VPN tunnels — the two endpoints need IPs to talk
- Layer 3 switches — uplinks between switches
- ISP allocations — sometimes your ISP gives you a /30 for your gateway
This is why network engineers love /30. Also, it's efficient. You're not grabbing a /24 and using 1% of it. You're taking exactly what you need.
What Happens If You Pick the Wrong Size?
This is where people get into trouble. Let's say you have a small office with 3 computers and decide to use a /30 because that's what you're used to. You assign .1 and .That said, 2 to two computers, then realize you have no addresses left for the third. Now you're subnetting again, reconfiguring everything, potentially breaking existing configs.
On the flip side, if you grab a /28 (14 usable IPs) for a simple router-to-router link, you're wasting 12 addresses that could have been used elsewhere. In large networks, that waste adds up fast.
How to Calculate a /30 (and Other Subnets)
You don't need to be a math whiz to figure this out. Here's the straightforward way:
- Start with 32 (total bits in an IPv4 address)
- Subtract the CIDR number (/30 in this case)
- That's your host bits: 32 - 30 = 2
- Raise 2 to that power: 2^2 = 4 total addresses
- Subtract 2 for reserved addresses: 4 - 2 = 2 usable
That formula works for any subnet. Day to day, want a /26? 32 - 26 = 6 host bits. 2^6 = 64 total, 62 usable. Simple.
Quick Reference for Common Subnets
- /30 — 4 total, 2 usable (point-to-point)
- /29 — 8 total, 6 usable (small links, 3-5 devices)
- /28 — 16 total, 14 usable (small office network)
- /27 — 32 total, 30 usable (growing team)
- /26 — 64 total, 62 usable (small department)
- /24 — 256 total, 254 usable (standard office network)
Common Mistakes People Make With /30 Subnets
Assuming All 4 Addresses Are Usable
This is the most frequent mistake. Newer network admins sometimes assign all four IPs to devices, then wonder why things aren't working. The network address and broadcast address simply don't respond to ping requests or accept connections. They're reserved by design.
Using /30 for Networks That Need to Grow
A /30 is great when you know you'll only ever need two devices. But if there's any chance you'll add a third device — even "just for testing" — grab a /29 instead. Yes, you're wasting some addresses, but it's cheaper than re-addressing later.
Confusing /30 With Private IP Ranges
The subnet size has nothing to do with whether an IP is public or private. 8 (public) or 192.1.A /30 can contain 8.Day to day, 8. Also, 8. Think about it: 168. Think about it: 1 (private). The /30 just defines how many addresses you have in that block, not what kind they are That alone is useful..
Forgetting the Gateway
In a /30, you've got two usable IPs. Sometimes it's reversed. One goes to device A, one goes to device B. That's why 2. But which one is the gateway? Sometimes the router takes .On the flip side, 1 and the far-end device takes . It depends on your design. Just make sure both sides agree, or your link won't come up.
Practical Tips for Working With /30
Plan before you assign. Know exactly which two devices need addresses, and document it. In a /30, you don't have room for "we'll figure it out later."
Use the lower address for the router. This isn't a hard rule, but it's a common convention. The router or gateway typically gets the first usable IP (.1), with the far-end device at .2. It makes troubleshooting easier when every link follows the same pattern Still holds up..
Document the network and broadcast addresses. It sounds obvious, but when you're deep in a config, it's easy to forget that .0 and .3 are off-limits. Write it down. Save yourself the headache.
Test with ping before assuming it's working. With only two usable addresses, if the link doesn't come up, you know immediately something's wrong. Ping from .1 to .2 and vice versa. If it fails, you've got a layer 1, layer 2, or layer 3 problem to chase down.
FAQ
Can I use a /30 for a home network?
Technically yes, but it's impractical. Think about it: a home network with multiple devices, phones, and smart gadgets needs more than 2 usable IPs. A /24 (254 usable) is the standard for home networks Less friction, more output..
What's the smallest subnet I can use?
A /31 and /32 exist, but they're edge cases. A /31 gives you 2 addresses with no reserved addresses (used in certain point-to-point scenarios), and a /32 is a single IP — essentially a host route. For most purposes, /30 is the smallest subnet you'll regularly use And that's really what it comes down to. Took long enough..
Honestly, this part trips people up more than it should And that's really what it comes down to..
Why do I lose 2 addresses in every subnet?
The network address identifies the subnet itself — it's like the street name for your network. The broadcast address is used to send data to everyone on the subnet at once. Both are required for the network to function properly Surprisingly effective..
Is /30 the same as 255.255.255.252?
Yes, exactly. The subnet mask 255.255.255.252 is the decimal representation of a /30. You might see either notation depending on what system or device you're working with.
Can I have more than 2 devices on a /30?
No. If you try to add a third device, you won't have an IP to assign it. Which means you have exactly 2 usable addresses. This is a hard limit, not a soft guideline.
The Bottom Line
A /30 gives you 4 total IP addresses, 2 usable — nothing more, nothing less. And it's the smallest practical subnet for connecting two devices, and it's the go-to choice for router-to-router links, VPN endpoints, and WAN connections. Use it when you need exactly two addresses. Don't use it when you might need more Worth keeping that in mind..
It's one of those things that seems small, but getting it right saves a lot of reconfiguring down the road.
