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Chapter 19
Configuring Dynamic ARP Inspection
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.
Beginning in privileged EXEC mode, follow these steps to configure the log buffer. This procedure is
optional.
Command
Step 1
configure terminal
Step 2
ip arp inspection log-buffer {entries
number | logs number interval
seconds}
78-17058-01
Purpose
Enter global configuration mode.
Configure the dynamic ARP inspection logging buffer.
By default, when dynamic ARP inspection is enabled, denied or dropped
ARP packets are logged. The number of log entries is 32. The number of
system messages is limited to 5 per second. The logging-rate interval is 1
second.
The keywords have these meanings:
•
For entries number, specify the number of entries to be logged in the
buffer. The range is 0 to 1024.
•
For logs number interval seconds, specify the number of entries to
generate system messages in the specified interval.
For logs number, the range is 0 to 1024. A 0 value means that the entry
is placed in the log buffer, but a system message is not generated.
For interval seconds, the range is 0 to 86400 seconds (1 day). A 0 value
means that a system message is immediately generated (and the log
buffer is always empty).
An interval setting of 0 overrides a log setting of 0.
The logs and interval settings interact. If the logs number X is greater than
interval seconds Y, X divided by Y (X/Y) system messages are sent every
second. Otherwise, one system message is sent every Y divided by X (Y/X)
seconds.
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Configuring Dynamic ARP Inspection
19-13
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