Chapter 26 IP Source Guard
3Configure trusted and untrusted ports, and specify the maximum number of DHCP packets that each port can receive per second.
4Configure static bindings.
26.1.2 ARP Inspection Overview
Use ARP inspection to filter unauthorized ARP packets on the network. This can prevent many kinds of
Figure 123 Example:
AB
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.
26.1.2.1 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 12 on page 123).
•They are stored only in volatile memory.
•They do not use the same space in memory that regular MAC address filters use.
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