/30 Subnet
2 usable hosts — point-to-point link
A /30 is the classic subnet for point-to-point links, providing exactly 2 usable host addresses. Every WAN link, router-to-router connection, and dedicated lease line traditionally uses a /30.
Common Use Cases
- → WAN point-to-point link between routers
- → BGP peering session
- → Dedicated leased line addressing
Example /30 Networks
| CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|
| 10.0.0.0/30 | 10.0.0.0 | 10.0.0.1 | 10.0.0.2 | 10.0.0.3 | 2 |
| 172.16.0.0/30 | 172.16.0.0 | 172.16.0.1 | 172.16.0.2 | 172.16.0.3 | 2 |
| 172.31.0.0/30 | 172.31.0.0 | 172.31.0.1 | 172.31.0.2 | 172.31.0.3 | 2 |
| 192.168.0.0/30 | 192.168.0.0 | 192.168.0.1 | 192.168.0.2 | 192.168.0.3 | 2 |
| 192.168.1.0/30 | 192.168.1.0 | 192.168.1.1 | 192.168.1.2 | 192.168.1.3 | 2 |
| 10.0.1.0/30 | 10.0.1.0 | 10.0.1.1 | 10.0.1.2 | 10.0.1.3 | 2 |
How /30 Compares
| Prefix | Total IPs | Usable Hosts | Subnet Mask | Typical Use |
|---|---|---|---|---|
| /27 | 32 | 30 | 255.255.255.224 | Small workgroup / management subnet |
| /28 | 16 | 14 | 255.255.255.240 | AWS NAT/endpoint dedicated subnet |
| /29 | 8 | 6 | 255.255.255.248 | Tiny server cluster or infra segment |
| /30 ◀ | 4 | 2 | 255.255.255.252 | WAN point-to-point link |
| /31 | 2 | 2 | 255.255.255.254 | Modern P2P links (RFC 3021) |
| /32 | 1 | 1 | 255.255.255.255 | Single host — firewall rules, host routes |
Frequently Asked Questions
How many IPs are in a /30?
A /30 subnet contains 4 total IP addresses and 2 usable host addresses. The network address (first IP) and broadcast address (last IP) are reserved and cannot be assigned to hosts.
What is the subnet mask for /30?
The subnet mask for a /30 is 255.255.255.252.
In CIDR notation, the prefix length /30 means
the first 30 bits of the address are the network portion.
The wildcard (inverse) mask is 0.0.0.3.
How many /30 subnets fit in a /29?
Exactly 2 — a /29 can be split into two /30 subnets of equal size. Each /30 subnet has 2 usable hosts, compared to 6 in the parent /29.