Administrator Guide

The following example shows an extended IP ACL in which the sequence numbers were assigned by the software. The filters were
assigned sequence numbers based on the order in which they were configured (for example, the first filter was given the lowest sequence
number). The show config command in IP ACCESS LIST mode displays the two filters with the sequence numbers 5 and 10.
Dell(config-ext-nacl)#deny tcp host 123.55.34.0 any
Dell(config-ext-nacl)#permit udp 154.44.123.34 0.0.255.255 host 34.6.0.0
Dell(config-ext-nacl)#show config
!
ip access-list extended nimule
seq 5 deny tcp host 123.55.34.0 any
seq 10 permit udp 154.44.0.0 0.0.255.255 host 34.6.0.0
Dell(config-ext-nacl)#
To view all configured 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 first example in Configure a Standard IP ACL Filter.
Configure Layer 2 and Layer 3 ACLs
Both Layer 2 and Layer 3 ACLs may be configured 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 filtered against an L2 ACL.
• When the system switches the packets, first the L3 ACL filters them, then the L2 ACL filters them.
• When the system switches the packets, the egress L3 ACL filters the packet.
For the following features, if you enable counters on rules that have already been configured 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 affected.
Table 6. L2 and L3 Filtering on Switched Packets
L2 ACL Behavior L3 ACL Behavior Decision on Targeted Traffic
Deny Deny L3 ACL denies.
Deny Permit L3 ACL permits.
Permit Deny L3 ACL denies.
Permit Permit L3 ACL permits.
NOTE: If you configure an interface as a vlan-stack access port, only the L2 ACL filters the packets. The L3 ACL applied
to such a port does not affect traffic. That is, existing rules for other features (such as trace-list, policy-based routing
[PBR], and QoS) are applied to the permitted traffic.
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 specified 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 configure ACL VLAN groups to combine all VLANs on which ACL
filtering 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.
Access Control Lists (ACLs) 113