/30 subnet mask (255.255.255.252)

A /30 network has 2 host bits, 4 addresses and 2 usable hosts. It is 1/64 of a /24.

/30 at a glance

Netmask: 255.255.255.252
Wildcard mask: 0.0.0.3
Hex mask: 0xFFFFFFFC
Binary mask: 11111111.11111111.11111111.11111100
Host bits: 2
Total addresses: 4
Usable hosts: 2 (minus network and broadcast)
Compared with a /24: 1/64 of a /24

Calculate a /30 in the subnet calculator

Typical uses of a /30

The /30 is the traditional point-to-point link mask: 4 addresses, 2 usable, one for each end of a WAN or router-to-router link. Many operators now use /31 instead, which saves half the space.

Example /30 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /30
10.0.0.0/30	10.0.0.0	10.0.0.1	10.0.0.2	10.0.0.3	10.0.0.4/30	calculate
172.16.0.0/30	172.16.0.0	172.16.0.1	172.16.0.2	172.16.0.3	172.16.0.4/30	calculate
192.168.1.0/30	192.168.1.0	192.168.1.1	192.168.1.2	192.168.1.3	192.168.1.4/30	calculate
203.0.113.0/30	203.0.113.0	203.0.113.1	203.0.113.2	203.0.113.3	203.0.113.4/30	calculate

The /30 boundary falls in the fourth octet, so /30 networks start every 4 in that octet (64 per /24): 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, ....

How many /30s fit

In a	Number of /30 subnets
/8	4,194,304
/16	16,384
/20	1,024
/24	64
/28	4

What a /30 contains

Smaller block	How many
/32	4

Splitting a /30

Into	Subnets	Usable hosts each
/31	2	2
/32	4	1

/30 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/30 allowed?	Usable after reservation
AWS VPC	/16 to /28	No	-
Azure VNet	/2 to /29	No	-
Google Cloud VPC	/4 to /29	No	-

Cloud providers reserve addresses in every subnet (first four and the last address (network, VPC router, DNS, future use, broadcast) on AWS), so the usable count there differs from the classic 2^n - 2.