Limiting The Rate Of Incoming Arp Packets - Cisco Catalyst 2975 Software Configuration Manual
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Chapter 21
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 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.
Unless you configure a rate limit on an interface, changing the trust state of the interface also changes
Note
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
Inspection Configuration Guidelines" section on page
Beginning in privileged EXEC mode, follow these steps to limit the rate of incoming ARP packets. This
procedure is optional.
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
ip arp inspection limit {rate pps [burst
interval seconds] | none}
Step 4
exit
OL-19720-02
21-6.
Purpose
Enter global configuration mode.
Specify the interface to be rate-limited, and enter interface
configuration mode.
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.
Return to global configuration mode.
Catalyst 2975 Switch Software Configuration Guide
Configuring Dynamic ARP Inspection
"Dynamic ARP
21-11
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