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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 15 Configuring Access Control
Using VACLs in Your Network
When you create a security ACL, you need to be careful because the statically configured ARP
inspection rules have a higher priority than the DAI checks of the DHCP bindings. Do not put a
permit
arp-inspection any any
clause in the security ACL because it will prevent any checks from occurring.
You can enable or disable DAI on a per-VLAN basis. If you configure the DAI ports as untrusted, you
must also configure them as DHCP-snooping untrusted ports. You should enable DHCP snooping in all
VLANs that have DAI enabled. Optionally, you can enable logging for the ARP packets that are denied
by DAI.
Note
DAI works best when enabled on VLANs where all (or most) of the IP address assignment is done using
DHCP.
If the static IP address assignments exist in a VLAN, you must configure the relevant ports as ARP
inspection-trusted ports or you must configure the static ARP inspection nubs to permit these MAC and
IP addresses.
Dynamic ARP Inspection Configuration Procedures
Note
We recommend that you enable high availability when using DAI, DHCP snooping, and IP source guard. If
high availability is not enabled, the clients have to renew their IP addresses for these features to work after a
switchover. For the configuration details on DHCP snooping and IP source guard, see
Chapter 33,
“Configuring DHCP Snooping and IP Source Guard.”
Note
Prior to software release 8.6(1), you could enable dynamic ARP inspection only on VLANs. In software
release 8.6(1) and later releases, you can enable dynamic ARP inspection on a per-port basis.
Before you configure DAI, you will need to enable dynamic ARP inspection on a per-port basis. Perform
this task in privileged mode:
Task
Command
Step 1
Make the security ACL mode port-based on the
host port.
set port security-acl
mod/port
port-based
Step 2
Enable DAI on the port using the CLI.
set security acl arp-inspection dynamic enable
port
mod/port
Step 3
Display the security ACL ARP inspection
configuration.
show security acl arp-inspection config
Step 4
Create an ACL using the
permit arp-inspection
any any
command (to redirect ARP packets to the
software).
set security acl ip dai permit dhcp-snooping
set security acl ip dai permit arp-inspection
any any
set security acl ip dai permit ip any any
commit security acl dai
Step 5
Map the ACL to the host port.
set security acl map dai
mod/port