Security Fundamentals Foundational ~5 min

Apply an ACL inbound on an interface

On R1, create standard ACL 10 permitting the 10.0.0.0/24 network, then apply it in on Gi0/0. Creating an ACL isn't enough. You must attach it to an interface for it to filter traffic.

Topology

Objectives

○A standard ACL permits 10.0.0.0 0.0.0.255 (numbered or named)
○That ACL applied in on Gi0/0

Hints

Hint 1, direction matters

in filters as packets arrive on the interface, out filters as they leave. Applying an ACL in the wrong direction is the #1 mistake. Always ask "which side of the interface will the packet be on when the router looks at it?".

Hint 2, wildcard mask

A wildcard is the inverse of a subnet mask. For a /24, the mask is 255.255.255.0, so the wildcard is 0.0.0.255. Anywhere the wildcard bit is 1, the ACL doesn't care about that bit.

Hint 3, full sequence

enable
configure terminal
 access-list 10 permit 10.0.0.0 0.0.0.255
 interface gi0/0
  ip access-group 10 in
  end

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Make R1 the HSRP active router

IP Services · ~8 min

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Write a standard numbered ACL

Security Fundamentals · ~6 min

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Apply an ACL inbound on an interface

Stuck on a lab, or not sure what to practice next?