Wildcard Masking
Wildcards are used with access lists to specify an individual host, a network, or a certain range of a network or networks. To understand a wildcard, you need to understand what a block size is; it’s used to specify a range of addresses. Some of the different block sizes available are 64, 32, 16, 8, and 4.
When you need to specify a range of addresses, you choose the next-largest block size for your needs. For example, if you need to specify 34 networks, you need a block size of 64. If you want to specify 18 hosts, you need a block size of 32. If you only specify 2 networks, then a block size of 4 would work.