Free CCNA Subnet Calculator
Type an IPv4 address with a CIDR prefix or a dotted-decimal mask and get the full subnet breakdown instantly — network, broadcast, usable host range, host count, wildcard mask and a binary view. No sign-up, runs entirely in your browser.
Accepted formats: 192.168.1.10/24 or 10.0.0.1 255.255.0.0
How subnetting works (the 30-second version)
A subnet mask splits an IP address into a network portion and a host portion. The /24 in 192.168.1.10/24 means the first 24 bits identify the network and the remaining 8 bits identify hosts on it — giving 28 − 2 = 254 usable addresses.
- Network address — the first address in the subnet; identifies the subnet itself, never assigned to a host.
- Broadcast address — the last address; traffic sent here reaches every host in the subnet.
- Usable range — everything between network and broadcast; the addresses you can hand out.
- Wildcard mask — the inverse of the subnet mask, used in ACLs and OSPF network statements.
- Binary view — bold bits are the network portion; this is exactly how routers see your address.
Subnetting for the CCNA 200-301 exam
Subnetting questions show up in Network Fundamentals and across troubleshooting scenarios. The exam expects you to work out masks, ranges and host counts quickly — often without a calculator. Drill the block sizes (256 − mask octet) until /25 = 126, /26 = 62, /27 = 30, /28 = 14, /29 = 6 and /30 = 2 hosts are reflex.
For the full method with worked examples and practice questions, see our CCNA subnetting guide.
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