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CHAPTER 25
IP Source Guard
25.1 Overview
Use IP source guard to filter unauthorized DHCP and ARP packets in your network.
IP source guard uses a binding table to distinguish between authorized and unauthorized DHCP and
ARP packets in your network. A binding contains these key attributes:
•MAC address
•VLAN ID
•IP address
• Port number
When the Switch receives a DHCP or ARP packet, it looks up the appropriate MAC address, VLAN ID,
IP address, and port number in the binding table. If there is a binding, the Switch forwards the
packet. If there is not a binding, the Switch discards the packet.
25.1.1 What You Can Do
•Use the IP Source Guard screen (Section 25.2 on page 194) to look at the current bindings for
DHCP snooping and ARP inspection.
•Use the IP Source Guard Static Binding screen (Section 25.3 on page 195) to manage static
bindings for DHCP snooping and ARP inspection.
•Use the DHCP Snooping screen (Section 25.4 on page 196) to look at various statistics about
the DHCP snooping database.
•Use this DHCP Snooping Configure screen (Section 25.5 on page 199) to enable DHCP
snooping on the Switch (not on specific VLAN), specify the VLAN where the default DHCP server
is located, and configure the DHCP snooping database.
•Use the DHCP Snooping Port Configure screen (Section 25.5.1 on page 201) to specify
whether ports are trusted or untrusted ports for DHCP snooping.
•Use the DHCP Snooping VLAN Configure screen (Section 25.5.2 on page 203) to enable DHCP
snooping on each VLAN and to specify whether or not the Switch adds DHCP relay agent option
82 information to DHCP requests that the Switch relays to a DHCP server for each VLAN.
•Use the ARP Inspection Status screen (Section 25.6 on page 204) to look at the current list of
MAC address filters that were created because the Switch identified an unauthorized ARP packet.
•Use the ARP Inspection VLAN Status screen (Section 25.7 on page 205) to look at various
statistics about ARP packets in each VLAN.
•Use the ARP Inspection Log Status screen (Section 25.8 on page 206) to look at log messages
that were generated by ARP packets and that have not been sent to the syslog server yet.
•Use the ARP Inspection Configure screen (Section 25.9 on page 207) to enable ARP inspection
on the Switch. You can also configure the length of time the Switch stores records of discarded
ARP packets and global settings for the ARP inspection log.
