Cisco Certified Network Associate (CCNA) Practice Exam

What is the wildcard mask for a specific host in ACL configuration?

1. 0.0.0.255

2. 255.255.255.255

3. 0.0.0.0

4. 255.255.255.0

The correct answer is: 0.0.0.0

The wildcard mask for a specific host in Access Control List (ACL) configuration is indeed 0.0.0.0. When you want to match a single host precisely in an ACL, you use a wildcard mask of 0.0.0.0, which effectively tells the router to match every bit of the IP address. This means that all bits in the address need to correspond exactly to the bits in the host IP being specified, allowing no variation. Therefore, the use of this wildcard mask means that only traffic to that exact IP address will be permitted or denied by the ACL. In contrast, other wildcard masks provided have different implications. For instance, a wildcard mask of 255.255.255.255 would match no bits, often used for special scenarios like a broadcast address, while 255.255.255.0 would allow for a subnet match, permitting all devices within that subnet to be considered as valid matches. Thus, only the 0.0.0.0 wildcard mask singularly represents the need for an exact match to a specific host in ACL configurations.