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21-11
Catalyst 2960 and 2960-S Switch Software Configuration Guide
OL-8603-09
Chapter 21 Configuring Dynamic ARP Inspection
Configuring Dynamic ARP Inspection
This example shows how to configure an ARP ACL called host2 on Switch A, to permit ARP packets
from Host 2 (IP address 1.1.1.1 and MAC address 0001.0001.0001), to apply the ACL to VLAN 1, and
to configure port 1 on Switch A as untrusted:
Switch(config)# arp access-list host2
Switch(config-arp-acl)# permit ip host 1.1.1.1 mac host 1.1.1
Switch(config-arp-acl)# exit
Switch(config)# ip arp inspection filter host2 vlan 1
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# no ip arp inspection trust
Limiting the Rate of Incoming ARP Packets
The switch CPU performs dynamic ARP inspection validation checks; therefore, the number of
incoming ARP packets is rate-limited to prevent a denial-of-service attack.
When the rate of incoming ARP packets exceeds the configured limit, the switch places the port in the
error-disabled state. The port remains in that state until you enable error-disabled recovery so that ports
automatically emerge from this state after a specified timeout period.
Note Unless you configure a rate limit on an interface, changing the trust state of the interface also changes
its rate limit to the default value for that trust state. After you configure the rate limit, the interface retains
the rate limit even when its trust state is changed. If you enter the no ip arp inspection limit interface
configuration command, the interface reverts to its default rate limit.
For configuration guidelines for rate limiting trunk ports and EtherChannel ports, see the “Dynamic ARP
Inspection Configuration Guidelines” section on page 21-6.
Beginning in privileged EXEC mode, follow these steps to limit the rate of incoming ARP packets. This
procedure is optional.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Specify the interface to be rate-limited, and enter interface configuration
mode.
Step 3
ip arp inspection limit {rate pps [burst
interval seconds] | none}
Limit the rate of incoming ARP requests and responses on the interface.
The default rate is 15 pps on untrusted interfaces and unlimited on
trusted interfaces. The burst interval is 1 second.
The keywords have these meanings:
• For rate pps, specify an upper limit for the number of incoming
packets processed per second. The range is 0 to 2048 pps.
• (Optional) For burst interval seconds, specify the consecutive
interval in seconds, over which the interface is monitored for a high
rate of ARP packets.The range is 1 to 15.
• For rate none, specify no upper limit for the rate of incoming ARP
packets that can be processed.
Step 4
exit Return to global configuration mode.