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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring Dynamic ARP Inspection
Configuring Dynamic ARP Inspection
To remove the ARP ACL, use the no arp access-list global configuration command. To remove the ARP
ACL attached to a VLAN, use the no ip arp inspection filter arp-acl-name vlan vlan-range global
configuration command.
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 gigabitethernet1/0/1
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.
Step 6
ip arp inspection smartlog Specify that whatever packets are currently being logged are also
smart-logged. By default, all dropped packets are logged.
Step 7
interface interface-id Specify the Switch A interface that is connected to Switch B, and enter
interface configuration mode.
Step 8
no ip arp inspection trust Configure the Switch A interface that is connected to Switch B as
untrusted.
By default, all interfaces are untrusted.
For untrusted interfaces, the switch intercepts all ARP requests and
responses. It verifies that the intercepted packets have valid IP-to-MAC
address bindings before updating the local cache and before forwarding
the packet to the appropriate destination. The switch drops invalid
packets and logs them in the log buffer according to the logging
configuration specified with the ip arp inspection vlan logging global
configuration command. For more information, see the “Configuring
the Log Buffer” section on page 1-13.
Step 9
end Return to privileged EXEC mode.
Step 10
show arp access-list [acl-name]
show ip arp inspection vlan vlan-range
show ip arp inspection interfaces
Verify your entries.
Step 11
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
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