ZyXEL ES-2108PWR User Guide - Page 166
ARP Inspection and MAC Address Filters, 1.1.2, Trusted vs. Untrusted Ports, 1.1.3, Syslog, 1.
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Chapter 21 IP Source Guard In this example, computer B tries to establish a connection with computer A. Computer X is in the same broadcast domain as computer A and intercepts the ARP request for computer A. Then, computer X does the following things: • It pretends to be computer A and responds to computer B. • It pretends to be computer B and sends a message to computer A. As a result, all the communication between computer A and computer B passes through computer X. Computer X can read and alter the information passed between them. 21.1.1.1 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. 21.1.1.2 Trusted vs. Untrusted Ports Every port is either a trusted port or an untrusted port for ARP inspection. The Switch does not discard ARP packets on trusted ports for any reason. The Switch discards ARP packets on untrusted ports if the sender's information in the ARP packet does not match any of the current bindings. 21.1.1.3 Syslog The Switch can send syslog messages to the specified syslog server (Chapter 29 on page 223) 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. 21.1.1.4 Configuring ARP Inspection Follow these steps to configure ARP inspection on the Switch. 1 Configure static bindings so the Switch can distinguish between authorized and unauthorized ARP packets. 2 Enable ARP inspection on the Switch. 3 Enable ARP inspection on each VLAN. 4 Configure trusted and untrusted ports, and specify the maximum number of ARP packets that each port can receive per second. 166 ES-2108 Series User's Guide