Concept Guide

Access Control Lists (ACLs)
This chapter describes access control lists (ACLs), prefix lists, and route-maps.
At their simplest, access control lists (ACLs), prefix lists, and route-maps permit or deny traffic based on MAC and/or IP
addresses. This chapter describes implementing IP ACLs, IP prefix lists and route-maps. For MAC ACLS, refer to Layer 2.
An ACL is essentially a filter containing some criteria to match (examine IP, transmission control protocol [TCP], or user
datagram protocol [UDP] packets) and an action to take (permit or deny). ACLs are processed in sequence so that if a packet
does not match the criterion in the first filter, the second filter (if configured) is applied. When a packet matches a filter, the
switch drops or forwards the packet based on the filter’s specified action. If the packet does not match any of the filters in the
ACL, the packet is dropped (implicit deny).
The number of ACLs supported on a system depends on your content addressable memory (CAM) size. For more information,
refer to User Configurable CAM Allocation and CAM Optimization. For complete CAM profiling information, refer to Content
Addressable Memory (CAM).
You can configure ACLs on VRF instances. In addition to the existing qualifying parameters, Layer 3 ACLs also incorporate VRF
ID as one of the parameters. Using this new capability, you can also configure VRF based ACLs on interfaces.
NOTE: You can apply Layer 3 VRF-aware ACLs only at the ingress level.
You can apply VRF-aware ACLs on:
● VRF Instances
● Interfaces
In order to configure VRF-aware ACLs on VRF instances, you must carve out a separate CAM region. You can use the cam-acl
command for allocating CAM regions. As part of the enhancements to support VRF-aware ACLs, the cam-acl command now
includes the following new parameter that enables you to allocate a CAM region: vrfv4acl.
The order of priority for configuring user-defined ACL CAM regions is as follows:
● V4 ACL CAM
● VRF V4 ACL CAM
● L2 ACL CAM
With the inclusion of VRF based ACLs, the order of precedence of Layer 3 ACL rules is as follows:
● Port/VLAN based PERMIT/DENY Rules
● Port/VLAN based IMPLICIT DENY Rules
● VRF based PERMIT/DENY Rules
● VRF based IMPLICIT DENY Rules
NOTE:
In order for the VRF ACLs to take effect, ACLs configured in the Layer 3 CAM region must have an implicit-permit
option.
You can use the ip access-group command to configure VRF-aware ACLs on interfaces. Using the ip access-group
command, in addition to a range of VLANs, you can also specify a range of VRFs as input for configuring ACLs on interfaces.
The VRF range is from 1 to 511. These ACLs use the existing V4 ACL CAM region to populate the entries in the hardware and do
not require you to carve out a separate CAM region.
NOTE: You can configure VRF-aware ACLs on interfaces either using a range of VLANs or a range of VRFs but not both.
Topics:
• IP Access Control Lists (ACLs)
• Important Points to Remember
• IP Fragment Handling
• Configure a Standard IP ACL
• Configure an Extended IP ACL
• Configure Layer 2 and Layer 3 ACLs
• Assign an IP ACL to an Interface
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