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21-5
Catalyst 2960 and 2960-S Switch Software Configuration Guide
OL-8603-09
Chapter 21 Configuring Dynamic ARP Inspection
Configuring Dynamic ARP Inspection
Logging of Dropped Packets
When the switch drops a packet, it places an entry in the log buffer and then generates system messages
on a rate-controlled basis. After the message is generated, the switch clears the entry from the log buffer.
Each log entry contains flow information, such as the receiving VLAN, the port number, the source and
destination IP addresses, and the source and destination MAC addresses.
You use the ip arp inspection log-buffer global configuration command to configure the number of
entries in the buffer and the number of entries needed in the specified interval to generate system
messages. You specify the type of packets that are logged by using the ip arp inspection vlan logging
global configuration command. For configuration information, see the “Configuring the Log Buffer”
section on page 21-13.
Configuring Dynamic ARP Inspection
These sections contain this configuration information:
• Default Dynamic ARP Inspection Configuration, page 21-5
• Dynamic ARP Inspection Configuration Guidelines, page 21-6
• Configuring Dynamic ARP Inspection in DHCP Environments, page 21-7 (required in DHCP
environments)
• Configuring ARP ACLs for Non-DHCP Environments, page 21-9 (required in non-DHCP
environments)
• Limiting the Rate of Incoming ARP Packets, page 21-11 (optional)
• Performing Validation Checks, page 21-12 (optional)
• Configuring the Log Buffer, page 21-13 (optional)
Default Dynamic ARP Inspection Configuration
Table 21-1 shows the default dynamic ARP inspection configuration.
Table 21-1 Default Dynamic ARP Inspection Configuration
Feature Default Setting
Dynamic ARP inspection Disabled on all VLANs.
Interface trust state All interfaces are untrusted.
Rate limit of incoming ARP packets The rate is 15 pps on untrusted interfaces, assuming that
the network is a switched network with a host
connecting to as many as 15 new hosts per second.
The rate is unlimited on all trusted interfaces.
The burst interval is 1 second.
ARP ACLs for non-DHCP environments No ARP ACLs are defined.
Validation checks No checks are performed.