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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 19 Configuring DHCP Features and IP Source Guard
Configuring IP Source Guard

Source IP Address Filtering

When IP source guard is enabled with this option, IP traffic is filtered based on the source IP address.
The switch forwards IP traffic when the source IP address matches an entry in the DHCP snooping
binding database or a binding in the IP source binding table.
When a DHCP snooping binding or static IP source binding is added, changed, or deleted on an interface,
the switch modifies the port ACL using the IP source binding changes, and re-applies the port ACL to
the interface.
If you enable IP source guard on an interface on which IP source bindings (dynamically learned by
DHCP snooping or manually configured) are not configured, the switch creates and applies a port ACL
that denies all IP traffic on the interface. If you disable IP source guard, the switch removes the port ACL
from the interface.

Source IP and MAC Address Filtering

When IP source guard is enabled with this option, IP traffic is filtered based on the source IP and MAC
addresses. The switch forwards traffic only when the source IP and MAC addresses match an entry in
the IP source binding table.
When IP source guard with source IP and MAC address filtering is enabled, the switch filters IP and
non-IP traffic. If the source MAC address of an IP or non-IP packet matches a valid IP source binding,
the switch forwards the packet. The switch drops all other types of packets except DHCP packets.
The switch uses port security to filter source MAC addresses. The interface can shut down when a
port-security violation occurs.
Configuring IP Source Guard
These sections contain this configuration information:
• Default IP Source Guard Configuration, page 19-16
• IP Source Guard Configuration Guidelines, page 19-17
• Enabling IP Source Guard, page 19-17

Default IP Source Guard Configuration

By default, IP source guard is disabled.