Zyxel OLT2412 [181/326] Arp inspection overview

Chapter 25 IP Source Guard

OLT2412 User’s Guide

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• 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 29 on page 215 for more information about DHCP relay

option 82.

When the DHCP server responds, the OLT 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 29 on page 215).

25.1.1.4 Configuring DHCP Snooping

Follow these steps to configure DHCP snooping on the OLT.

1 Enable DHCP snooping on the OLT.

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.

25.1.2 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 50 Example: Man-in-the-middle Attack

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.