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Catalyst 3560 Switch Software Configuration Guide
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Chapter 22 Configuring Dynamic ARP Inspection
Configuring Dynamic ARP Inspection
To disable checking, use the no ip arp inspection validate [src-mac] [dst-mac] [ip] global
configuration command. To display statistics for forwarded, dropped, and MAC and IP validation failure
packets, use the show ip arp inspection statistics privileged EXEC command.
Configuring the Log Buffer
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.
A log-buffer entry can represent more than one packet. For example, if an interface receives many
packets on the same VLAN with the same ARP parameters, the switch combines the packets as one entry
in the log buffer and generates a single system message for the entry.
If the log buffer overflows, it means that a log event does not fit into the log buffer, and the display for
the show ip arp inspection log privileged EXEC command is affected. A -- in the display appears in
place of all data except the packet count and the time. No other statistics are provided for the entry. If
you see this entry in the display, increase the number of entries in the log buffer or increase the logging
rate.
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 ip arp inspection validate
{[src-mac] [dst-mac] [ip]}
Perform a specific check on incoming ARP packets. By default, no checks
are performed.
The keywords have these meanings:
• For src-mac, check the source MAC address in the Ethernet header
against the sender MAC address in the ARP body. This check is
performed on both ARP requests and responses. When enabled, packets
with different MAC addresses are classified as invalid and are dropped.
• For dst-mac, check the destination MAC address in the Ethernet header
against the target MAC address in ARP body. This check is performed
for ARP responses. When enabled, packets with different MAC
addresses are classified as invalid and are dropped.
• For ip, check the ARP body for invalid and unexpected IP addresses.
Addresses include 0.0.0.0, 255.255.255.255, and all IP multicast
addresses. Sender IP addresses are checked in all ARP requests and
responses, and target IP addresses are checked only in ARP responses.
You must specify at least one of the keywords. Each command overrides the
configuration of the previous command; that is, if a command enables src
and dst mac validations, and a second command enables IP validation only,
the src and dst mac validations are disabled as a result of the second
command.
Step 3 exit Return to privileged EXEC mode.
Step 4 show ip arp inspection vlan
vlan-range
Verify your settings.
Step 5 copy running-config startup-config (Optional) Save your entries in the configuration file.