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Chapter33 Configuring Network Security with ACLs
Understanding ACLs
Figure33-1 Using ACLs to Control Traffic to a Network
Port ACLs
You can also apply ACLs to Layer 2 interfaces on a switch. Port ACLs are supported on physical
interfaces and EtherChannel interfaces.
The following access lists are supported on Layer 2 interfaces:
•Standard IP access lists using source addresses
•Extended IP access lists using source and destination addre sses and optional protocol type
information
•MAC extended access lists using source and destination MAC addresses and optional protocol type
information
As with router ACLs, the switch examines ACLs associated with features configured on a given interface
and permits or denies packet forwarding based on how the packet matches the entries in the ACL. In the
example in Figure 33-1, if all workstations were in the same VLAN, ACLs applied at the Layer 2 input
would allow Host A to access the Human Resources network, but prevent Host B from accessing t he
same network.
When you apply a port ACL to a trunk port, the ACL filters traffic on all VLANs present on the trunk
port. When you apply a port ACL to a port with voice VLAN, the ACL filters traffic on both da ta and
voice VLANs.
With port ACLs, you can filter IP traffic by using IP access lists and non-IP traffic by using MAC
addresses. You can filter both IP and non-IP traffic on the same Layer 2 interface by applying both an IP
access list and a MAC access list to the interface.
Note You cannot apply more than one IP access list and one MAC access list to a Layer 2 interfac e. If an IP
access list or MAC access list is already configured on a Layer 2 interface and you apply a new IP access
list or MAC access list to the interface, the new ACL replaces the previously configured one.
Si Host A
Host B
94152
Research &
Development
network
= ACL denying traffic from Host B
and permitting traffic from Host A
= Packet
Catalyst 4500 series switch
Human
Resources
network