Setup Guide

To view all congured IP ACLs and the number of packets processed through the ACL, use the show ip accounting access-list
command in EXEC Privilege mode, as shown in the rst example in Congure a Standard IP ACL Filter.
Congure Layer 2 and Layer 3 ACLs
Both Layer 2 and Layer 3 ACLs may be congured on an interface in Layer 2 mode.
If both L2 and L3 ACLs are applied to an interface, the following rules apply:
• When the system routes the packets, only the L3 ACL governs them because they are not ltered against an L2 ACL.
• When the system switches the packets, rst the L3 ACL lters them, then the L2 ACL lters them.
• When the system switches the packets, the egress L3 ACL lters the packet.
For the following features, if you enable counters on rules that have already been congured and a new rule is either inserted or prepended,
all the existing counters are reset:
• L2 ingress access list
• L3 egress access list
• L2 egress access list
If a rule is simply appended, existing counters are not aected.
Table 6. L2 and L3 Filtering on Switched Packets
L2 ACL Behavior L3 ACL Behavior Decision on Targeted Trac
Deny Deny L3 ACL denies.
Deny Permit L3 ACL permits.
Permit Deny L3 ACL denies.
Permit Permit L3 ACL permits.
NOTE: If you congure an interface as a vlan-stack access port, only the L2 ACL lters the packets. The L3 ACL applied to such
a port does not aect trac. That is, existing rules for other features (such as trace-list, policy-based routing [PBR], and QoS)
are applied to the permitted trac.
For information about MAC ACLs, refer to Layer 2.
Using ACL VLAN Groups
Use an ACL VLAN group to optimize ACL CAM usage by minimizing the number of CAM entries when you apply an egress IP ACL on the
member interfaces of specied VLANs.
When you apply an ACL on individual VLANs, the amount of CAM space required increases greatly because the ACL rules are saved for
each VLAN ID. To avoid excessive use of the CAM space, you can congure ACL VLAN groups to combine all VLANs on which ACL
ltering criteria is applied in a single class ID instead of multiple VLAN IDs.
NOTE
: CAM optimization applies only when you use an ACL VLAN group; it does not apply if you apply an ACL on individual
VLANs.
Guidelines for Conguring ACL VLAN Groups
Keep the following points in mind when you congure ACL VLAN groups:
• The VLAN member interfaces, on which the ACL in an ACL VLAN group is applied, function as restricted interfaces. The ACL VLAN
group name identies the group of VLANs on which hierarchical ltering is performed.
Access Control Lists (ACLs)
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