IPv4 subnet calculator
Enter an address with its prefix or mask. See the block it belongs to, the usable host range, the masks you need for router configs, and how the block splits into smaller subnets.
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Split this block
How to use it
Three steps
- Type an address and prefix. For example 192.168.10.77/26. You can also type a dotted mask such as 10.0.0.0 255.255.252.0, or type just the address and pick the prefix from the list.
- Read the block. The calculator finds the block the address belongs to: its network address, first and last usable addresses, broadcast address and number of usable hosts.
- Split it if you need to. Choose a smaller block size to list every subnet inside it, and download the list as CSV.
Questions
Good to know
How many usable hosts does a subnet have?
Total addresses minus two: the network address and the broadcast address can't be given to a device. A /24 has 256 addresses and 254 usable hosts; a /29 has 8 and 6 usable; a /30 has 4 and 2 usable.
What is special about /31 and /32?
A /31 has two addresses and no broadcast address, so both can be used on a point-to-point link (RFC 3021). A /32 is a single address, often used for a router loopback.
What is a wildcard mask?
It is the subnet mask with every bit flipped. For a /26 the subnet mask is 255.255.255.192 and the wildcard mask is 0.0.0.63. Cisco access lists and OSPF network statements use wildcard masks.
Why does it say my address is inside a block?
If you type 192.168.10.77/26, the address 192.168.10.77 is a host inside the block 192.168.10.64/26. The results show that block, which is what you configure on the router.
What do private, CGNAT and documentation ranges mean?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are private ranges for internal networks. 100.64.0.0/10 is shared space for carrier-grade NAT. 192.0.2.0/24, 198.51.100.0/24 and 203.0.113.0/24 are reserved for documentation and examples.
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Open the tool/24 planner
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Open the toolIP spreadsheet checker
Find duplicates, overlaps and typos in an Excel or CSV list.
Open the tool
Still tracking IPs in a spreadsheet?
IPAM Enterprise keeps every /24, block, customer and circuit in one portal, and checks each assignment for overlaps before it is saved.