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33-4
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter 33 Configuring Network Security with ACLs
Understanding ACLs
Figure 33-1 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 addresses 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 the
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 data 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 interface. 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