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244
26.11.2.2 Trusted vs. Untrusted Ports
Every port is either a trusted port or an untrusted port for ARP inspection. This setting is
independent of the trusted/untrusted setting for DHCP snooping. You can also specify the maximum
rate at which the Switch receives ARP packets on untrusted ports.
The Switch does not discard ARP packets on trusted ports for any reason.
The Switch discards ARP packets on untrusted ports in the following situations:
• The sender’s information in the ARP packet does not match any of the current bindings.
• The rate at which ARP packets arrive is too high.
26.11.2.3 Syslog
The Switch can send syslog messages to the specified syslog server (Chapter 42 on page 351)
when it forwards or discards ARP packets. The Switch can consolidate log messages and send log
messages in batches to make this mechanism more efficient.
26.11.2.4 Configuring ARP Inspection
Follow these steps to configure ARP inspection on the Switch.
1 Configure DHCP snooping. See Section 26.11.1.4 on page 243.
Note: It is recommended you enable DHCP snooping at least one day before you enable
ARP inspection so that the Switch has enough time to build the binding table.
2 Enable ARP inspection on each VLAN.
3 Configure trusted and untrusted ports, and specify the maximum number of ARP packets that each
port can receive per second.
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