Calculator inputs
Choose a mode. Only its relevant fields will appear.
Network and host bit guide
Move the slider to visualize the IPv4 network and host boundary.
Formula used
Special rules override traditional host formulas for /31, /32, /127, and /128 networks.
How to use this calculator
1. Choose a mode
Select subnetting, range conversion, VLSM, comparison, membership, wildcard, conversion, or bulk analysis.
2. Enter network data
Use CIDR notation where possible. Examples include 192.168.1.10/24 and 2001:db8::1/64.
3. Adjust rules
Enable RFC 3021 for point-to-point /31 networks. Choose whether network and broadcast addresses count as usable.
4. Calculate and export
Review the result, filter tables, copy values, download data, or print the page as a PDF.
Network planning guide
Understanding an IP range
An IP range is a continuous sequence of addresses. A subnet describes an aligned range using a network address and prefix length. The prefix identifies fixed network bits. Remaining bits identify hosts or interfaces inside that network.
How CIDR notation works
CIDR joins an address and prefix, such as 192.168.1.0/24. A /24 fixes twenty-four bits. Eight bits remain. That creates 256 total IPv4 addresses. Traditional addressing reserves the first and last addresses.
Network and broadcast addresses
The network address has all host bits set to zero. The broadcast address has all host bits set to one. IPv6 does not use broadcast. It relies on multicast and anycast behavior instead.
Public and private addresses
Private IPv4 ranges support internal networks. They include 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Public routing normally requires globally unique addresses. Several additional ranges are reserved for documentation, benchmarking, multicast, and special protocols.
Variable Length Subnet Masks
VLSM assigns different prefix sizes to different requirements. Large departments receive larger blocks. Small links receive smaller blocks. Sorting by required size reduces fragmentation. Allocation must stay aligned to each subnet boundary.
Route aggregation
Aggregation combines adjacent, aligned networks into shorter prefixes. A correct summary simplifies routing tables. A broad summary can also include unused addresses. Always inspect the summarized range before deploying firewall or routing rules.
Special prefixes
A /32 identifies one IPv4 address. A /31 can support two point-to-point endpoints under RFC 3021. A /30 remains common for traditional point-to-point links. IPv6 commonly uses /64 for local networks, /127 for point-to-point links, and /128 for one interface.
Frequently asked questions
What is an IP range?
An IP range is a continuous sequence between a starting and ending address. A CIDR block is an aligned range represented by an address and prefix.
What does CIDR notation mean?
CIDR notation shows an address followed by fixed network bits. For example, /24 leaves eight IPv4 host bits.
What is the difference between /24 and /16?
A /24 contains 256 IPv4 addresses. A /16 contains 65,536 addresses. The /16 network is 256 times larger.
How many usable hosts are in a subnet?
Traditional IPv4 subnets use 2^host-bits minus two. Special /31 and /32 rules differ. IPv6 does not reserve a broadcast address.
Can a /31 subnet contain usable addresses?
Yes. RFC 3021 permits both /31 addresses on point-to-point links. Traditional LAN assumptions should not be applied there.
How is an IP range converted into CIDR blocks?
The range is divided into the largest aligned power-of-two blocks that fit. The process repeats until the ending address is covered.
What is a wildcard mask?
A wildcard mask is the inverse of a subnet mask. It is commonly used in access-control lists and routing configurations.
Does IPv6 have broadcast addresses?
No. IPv6 replaces broadcast behavior with multicast groups. Neighbor discovery and other protocols use scoped multicast addresses.