ZyXEL Communications ES-2048, User Manual

Page: 174 / 306

Chapter 21 IP Source Guard
ES-2048 User’s Guide
174
21.1.2.1 ARP Inspection and MAC Address Filters
When the Switch identifies an unauthorized ARP packet, it automatically creates a MAC
address filter to block traffic from the source MAC address and source VLAN ID of the
unauthorized ARP packet. You can configure how long the MAC address filter remains in the
Switch.
These MAC address filters are different than regular MAC address filters (
Chapter 10 on page
99 ).
• 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 and commands, not in the MAC
Address Filter screens and commands.
21.1.2.2 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.
21.1.2.3 Syslog
The Switch can send syslog messages to the specified syslog server ( Chapter 29 on page 243 )
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.
21.1.2.4 Configuring ARP Inspection
Follow these steps to configure ARP inspection on the Switch.
1 Configure DHCP snooping. See Section 21.1.1.4 on page 173 .
"
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.