CIDR Calculator

Enter an IP or CIDR block and see the full breakdown, bit by bit.

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Paste a full CIDR like 10.20.0.0/22 into the IP field — the prefix is picked up automatically.

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Cloud Reserved IP FAQ

How many IP addresses does AWS reserve in each VPC subnet?

AWS reserves 5 IP addresses in every VPC subnet: the network address (.0), the VPC router (.1), the DNS server (.2), a future-use address (.3), and the broadcast address (the last address in the block). A /24 subnet with 256 addresses therefore has 251 usable IPs.

How many IP addresses does Azure reserve in each subnet?

Azure reserves 5 IP addresses per subnet: the network address, the default gateway (.1), two addresses mapped for Azure DNS (.2 and .3), and the broadcast address (the last address in the block).

How many IP addresses does Google Cloud (GCP) reserve in each subnet?

Google Cloud reserves 4 IP addresses per subnet: the network address, the default gateway (.1), a second-to-last reserved address, and the broadcast address (the last address in the block).

What is the difference between total addresses and usable hosts?

Total addresses is the full size of the block (232-prefix). Usable hosts subtracts the network and broadcast address for standard subnets, or subtracts every address a selected cloud provider reserves for its own networking services when AWS, Azure or GCP is selected above.