The wildcard mask 0.0.0.255 stipulates that the very first three octets must match exactly, but the fourth octet does not need to match. In this example, ACL 10 needs an ACE that permits all hosts in the 192.168.1.0/24 network.

The resulting ACE in ACL 10 would be access-list 10 permit 192.168.1.1 0.0.0.0. Therefore, when the ACE is processed, the wildcard mask will permit only the 192.168.1.1 address. The 0.0.0.0 wildcard mask stipulates that every bit must match exactly. Table 4-3 Wildcard to Match a Host Example Table 4-3 lists, in decimal and binary, the host IPv4 address, the wildcard mask, and the permitted IPv4 address. To match a specific host IPv4 address, a wildcard mask consisting of all zeros (that is, 0.0.0.0) is required. Recall that 0 equals a match, and 1 equals ignore. Say that ACL 10 needs an ACE that only permits the host with IPv4 address 192.168.1.1. In this example, the wildcard mask is used to match a specific host IPv4 address.

The following sections provide examples to help you learn how wildcard masks are used to filter traffic for one host, one subnet, and a range IPv4 addresses. Using wildcard masks takes some practice. Ignore the 6 leftmost bits of the last octet Match the 4 leftmost bits of the last octet Match the 2 leftmost bits of the last octet

Table 4-2 lists some examples of wildcard masks and what they would match and ignore. Wildcard mask bit 1: Ignore the corresponding bit value in the address. Wildcard mask bit 0: Match the corresponding bit value in the address. Wildcard masks use the following rules to match binary 1s and 0s: Unlike with a subnet mask, in which binary 1 is equal to a match, and binary 0 is not a match, with a wildcard mask, the reverse is true. However, a wildcard mask and a subnet mask differ in the way they match binary 1s and 0s. Wildcard masks are also used by the Open Shortest Path First (OSPF) routing protocol.Ī wildcard mask is similar to a subnet mask in that it uses the ANDing process to identify which bits in an IPv4 address to match. An IPv4 ACE uses a 32-bit wildcard mask to determine which bits of the address to examine for a match.

This section explains how ACLs use wildcard masks. In the previous section, you learned about the purpose of ACL. In this section, you will learn how to calculate the inverse wildcard mask. A wildcard mask is similar to a subnet mask but the reverse.

Instal the last version for ios MASKA