Cisco Catalyst 3560-X Series, Software Configuration Manual

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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 1 Configuring DHCP Features and IP Source Guard
Displaying DHCP Snooping Information
Displaying DHCP Snooping Information
Note If DHCP snooping is enabled and an interface changes to the down state, the switch does not delete the
statically configured bindings.
Understanding IP Source Guard
IPSG is a security feature that restricts IP traffic on nonrouted, Layer 2 interfaces by filtering traffic
based on the DHCP snooping binding database and on manually configured IP source bindings. You can
use IP source guard to prevent traffic attacks if a host tries to use the IP address of its neighbor.
You can enable IP source guard when DHCP snooping is enabled on an untrusted interface. After IPSG
is enabled on an interface, the switch blocks all IP traffic received on the interface except for DHCP
packets allowed by DHCP snooping. A port access control list (ACL) is applied to the interface. The port
ACL allows only IP traffic with a source IP address in the IP source binding table and denies all other
traffic.
Note
The port ACL takes precedence over any router ACLs or VLAN maps that affect the same interface.
The IP source binding table has bindings that are learned by DHCP snooping or are manually configured
(static IP source bindings). An entry in this table has an IP address, its associated MAC address, and its
associated VLAN number. The switch uses the IP source binding table only when IP source guard is
enabled.
IPSG is supported only on Layer 2 ports, including access and trunk ports.You can configure IPSG with
source IP address filtering or with source IP and MAC address filtering.
These sections contain this information:
•
Source IP Address Filtering, page 1-17
•
Source IP and MAC Address Filtering, page 1-17
•
IP Source Guard for Static Hosts, page 1-17
Table 1-2 Commands for Displaying DHCP Information
Command Purpose
show ip dhcp snooping Displays the DHCP snooping configuration for a switch
show ip dhcp snooping binding Displays only the dynamically configured bindings in the DHCP snooping binding
database, also referred to as a binding table.
show ip dhcp snooping database Displays the DHCP snooping binding database status and statistics.
show ip dhcp snooping statistics Displays the DHCP snooping statistics in summary or detail form.
show ip source binding Display the dynamically and statically configured bindings.