Chapter 18 IP Source Guard
These MAC address filters are different than regular MAC address filters.
•They are stored only in volatile memory.
•They do not use the same space in memory that regular MAC address filters use.
•They appear only in the ARP Inspection screens.
18.3.2.2Trusted 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.
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.
18.3.2.3Syslog
The Switch can send syslog messages to the specified syslog server (Chapter 21 on page 133) 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.
18.3.2.4 Configuring ARP Inspection
Follow these steps to configure ARP inspection on the Switch.
1Configure DHCP snooping. See Section 18.3.1.3 on page 105.
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.
2Enable ARP inspection on each VLAN.
3Configure trusted and untrusted ports.
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