Wildcard Mask Calculator

Instantly convert a subnet mask to its wildcard mask equivalent. An essential tool for configuring Access Control Lists (ACLs) and some routing protocols.

Select Subnet Mask

Choose a subnet mask or CIDR prefix to calculate the corresponding wildcard mask.

Understanding Wildcard Masks

A wildcard mask is a 32-bit quantity used in networking to specify a range of IP addresses. It is, in essence, an inverted subnet mask. While a subnet mask uses binary 1s to identify the network portion of an address, a wildcard mask uses binary 0s for the same purpose.

How It Works

In a wildcard mask, a binary 0 indicates that the corresponding bit in the IP address must match exactly. A binary 1 indicates that the corresponding bit can be ignored (it can be a "wildcard"). This "match" or "don't care" logic is fundamental to its operation.

For example, to match only the host 192.168.1.1, the wildcard mask would be 0.0.0.0. To match any host in the 192.168.1.0/24 network, the wildcard mask would be 0.0.0.255.

Primary Use Cases

Wildcard masks are most commonly encountered when configuring Access Control Lists (ACLs) on routers and firewalls to permit or deny traffic from specific IP addresses or ranges. They are also used by some routing protocols like EIGRP and OSPF to identify which interfaces should participate in the routing process. Our Subnet Calculator can help you find the initial subnet mask you need.