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Feb 9 / Greg

Cisco – Absence Of A Wildcard Mask In An ACL

If I have a standard ACL entry like this:

access-list 98 deny
access-list 98 permit any

and I apply it to an interface. What addressing does this block?

One might think that leaving off the wildcard mask would use the classful boundary(/8 or of the addressing…but one would be wrong. In IOS if you leave off the wildcard mask a wildcard mask of is assumed. This means the address is considered a host address(a single IP address). This means the first line equates to :

access-list 98 deny


access-list 98 deny host
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