172.31.0.0/16 (AWS Default VPC)
PrivateRFC 1918
172.31.0.0/16 at a glance
| CIDR block | 172.31.0.0/16 |
|---|---|
| First address | 172.31.0.0 |
| Last address | 172.31.255.255 |
| Total addresses | 65,536 |
| Subnet mask | 255.255.0.0 |
| Prefix length | /16 |
| Type | Private |
| Publicly routable | No |
| Defined in | RFC 1918 |
Open in CIDR calculator/16 subnet details
What is 172.31.0.0/16 used for?
172.31.0.0/16 is the CIDR block of the default VPC that AWS creates in every region. Its default subnets are /20s, one per Availability Zone (172.31.0.0/20, 172.31.16.0/20, 172.31.32.0/20…). Because every account has the same range, default VPCs cannot be peered with each other.
Common subnets of 172.31.0.0/16
Overlaps and conflicts
- Inside 172.16.0.0/12
FAQ
What subnets does the AWS default VPC use?
One /20 per Availability Zone: 172.31.0.0/20, 172.31.16.0/20, 172.31.32.0/20, and so on. Each has 4,091 usable addresses after AWS reserves 5.
Can I peer two AWS default VPCs?
No. Every default VPC uses 172.31.0.0/16, and VPC peering does not allow overlapping CIDR blocks. Create a custom VPC with a different range instead.