ZyXEL ES-3124PWR User Guide - Page 195
ARP Inspection Overview
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Chapter 24 IP Source Guard 24.1.1.3 DHCP Relay Option 82 Information The Switch can add information to DHCP requests that it does not discard. This provides the DHCP server more information about the source of the requests. The Switch can add the following information: • Slot ID (1 byte), port ID (1 byte), and source VLAN ID (2 bytes) • System name (up to 32 bytes) This information is stored in an Agent Information field in the option 82 field of the DHCP headers of client DHCP request frames. See Chapter 28 on page 227 for more information about DHCP relay option 82. When the DHCP server responds, the Switch removes the information in the Agent Information field before forwarding the response to the original source. You can configure this setting for each source VLAN. This setting is independent of the DHCP relay settings (Chapter 28 on page 227). 24.1.1.4 Configuring DHCP Snooping Follow these steps to configure DHCP snooping on the Switch. 1 Enable DHCP snooping on the Switch. 2 Enable DHCP snooping on each VLAN, and configure DHCP relay option 82. 3 Configure trusted and untrusted ports, and specify the maximum number of DHCP packets that each port can receive per second. 4 Configure static bindings. 24.1.2 ARP Inspection Overview Use ARP inspection to filter unauthorized ARP packets on the network. This can prevent many kinds of man-in-the-middle attacks, such as the one in the following example. Figure 104 Example: Man-in-the-middle Attack A B X 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. ES-3124 Series User's Guide 195