Specifications

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Chapter 26 Configuring Network Security with ACLs
Understanding 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. ACLs can only be
applied to Layer 2 interfaces in the inbound direction. In the example in Figure 26-1, 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.
Figure 26-1 Using ACLs to Control Traffic to a 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.
VLAN Maps
You use VLAN ACLs or VLAN maps to filter traffic between devices in the same VLAN. When a VLAN
map is applied to a VLAN, all packets being forwarded in the VLAN are checked against the VLAN
map, VLAN maps are used for security packet filtering. VLAN maps are not defined by direction (input
or output).
Host A
Host B
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Research &
Development
network
= ACL denying traffic from Host B
and permitting traffic from Host A
= Packet
Catalyst 2970
switch
Human
Resources
network