To understand the difference between subnet mask and wildcard mask you need to understand what they are and where they are used.
Starting with subnet mask, subnet stands for a sub-network and mask here is something that reveals information about a sub-network. Subnet is a part of IP internetwork or you can say there one or more subnets that resides in an internetwork. Subnet mask in terms, tells about the intent of the subnet design.
Firstly, the mask divides address into 2 parts, prefix and host, with a host part defining the size of the subnet. Then, classes (A, B or C) further divides the addresses in a subnet, breaking the prefix part into the network and subnet parts. The subnet part represents the no. of subnets that could be present inside one classful IP network, assuming that one mask is used throughout the classful network. Subnet mask can be written as 32-bit binary numbers.
Subnet mask defines the prefix part of the IP address in a subnet. The prefix part must be the same value for all addresses in a subnet. In fact, a single subnet can be defined as all IPv4 addresses that have the same value in the prefix part of their IPv4 addresses. Thus, the prefix part identifies the address that reside in the same subnet.
Uses of subnet mask:
- Defines the size of the prefix (combine network and subnet) part of the addresses in a subnet.
- Defines the no. of the host bits of the address per subnet.
- Can be used to calculate the total no. of hosts per subnet.
- Provides a means for the network designer to communicate the design details such as the number of subnet and host bits, to the devices in the network.
- Can also be used to calculate the no. of subnets that can exist in the entire classful network.
- Can be used in binary calculations of subnet ID and their broadcast address.
Whereas, wildcard mask is also a 32-bit binary number like subnet mask, but the subnet part is replaced with binary 0’s instead of 1’s. Wildcard mask are generally used as a search pattern by IOS software for traffic filtering purposes. Wildcard Mask is used to indicate to the IOS software whether to check or ignore corresponding IP address bits when comparing the address bits in an access list entry. It is used with OSPF and EIGRP implementation.