Why Use Wildcard Masks with ACLs

This video, Keith Barker covers how to filter or block an entire subnet or range of addresses with wildcard masks on an access control list (ACL). He begins with a short description of a wildcard mask and then shows you how to apply it to a standard ACL.

Standard ACLs are a set of rules that routers follow when they’re deciding to allow or deny packets based on their source address. With ACLs, administrators have complete control over what gets forwarded through the router or dropped.

In some cases, administrators may want to deny a single source address, which they can do with a simple deny statement.

Other times, administrators want to block an entire range of addresses. For that task, they could either write out hundreds (or thousands!) of deny statements — or they can use a wildcard mask to filter for an entire block of source IP addresses.

Start learning with CBT Nuggets:

[danielfey]

Thank you for explaining wildcard masks with ACLs!

[yparam]

Very useful and knowledgeable video, thank you.

[abcbirdsandbees]

a subnet mask denotes a network, while a wildcard mask is used for a range of ips.

[ChasedWheels]

Thanks Keith. It was very informative.

[oleggorenkov]

Why we use a wildcard mask is understandable. Why a wildcard mask and not a mask is unclear.