ZyXEL GS1920 Series User Guide - Page 221

ARP Inspection Overview

Page 221 highlights

Chapter 25 IP Source Guard 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. 25.10.2 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 160 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. 25.10.2.1 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 12 on page 110). • 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, not in the MAC Address Filter screens. GS1920 Series User's Guide 221

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Chapter 25 IP Source Guard
GS1920 Series User’s Guide
221
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.
25.10.2
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 160
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.
25.10.2.1
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 12 on page 110).
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, not in the
MAC Address Filter
screens.
A
X
B