A /22 subnet uses 22 bits for the network portion of an IPv4 address, leaving 10 bits for host addressing. This produces 1,024 total IP addresses and 1,022 usable hosts. A /22 spans exactly 4 consecutive /24 blocks, making it a natural choice when a single /24 is too small but a /20 is overkill.
x.x.x.0 (third octet must be multiple of 4: .0, .4, .8, .12, …)
Broadcast address
x.x.3.255 (last address in the 4-block span)
Binary mask
11111111.11111111.11111100.00000000
AWS usable hosts
1,019 (AWS reserves 5 IPs per subnet)
A /22 is Four /24s Merged
Conceptually, a /22 is exactly four /24 subnets aggregated into one block. The third octet of the network address must start on a multiple of 4 — so valid /22 networks include 10.0.0.0/22, 10.0.4.0/22, 10.0.8.0/22, etc. This makes /22 a useful summary route for announcing groups of /24s in BGP.
Example /22 Ranges in 10.0.0.0/16
Subnet
Range
Spans /24s
AWS Usable
10.0.0.0/22
10.0.0.0 – 10.0.3.255
.0, .1, .2, .3
1,019
10.0.4.0/22
10.0.4.0 – 10.0.7.255
.4, .5, .6, .7
1,019
10.0.8.0/22
10.0.8.0 – 10.0.11.255
.8, .9, .10, .11
1,019
10.0.12.0/22
10.0.12.0 – 10.0.15.255
.12, .13, .14, .15
1,019
Common Use Cases for /22 Subnets
Large office VLANs — fits up to 1,022 workstations, phones, and IoT devices in a single broadcast domain
Azure workload subnets — 1,019 usable IPs (Azure also reserves 5); good for large VM scale sets
Campus wireless networks — a /22 gives one subnet for an entire building's Wi-Fi clients
Development environments — large shared subnet for dev teams with many containers/VMs
BGP route summarisation — aggregate four /24s into one announcement to reduce routing table size