Chapter 22 Configuring DHCP Features and IP Source Guard

Configuring IP Source Guard

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 22-17

IP Source Guard Configuration Guidelines, page 22-17

Enabling IP Source Guard, page 22-18

Default IP Source Guard Configuration

By default, IP source guard is disabled.

IP Source Guard Configuration Guidelines

These are the configuration guides for IP source guard:

You can configure static IP bindings only on nonrouted ports. If you enter the ip source binding mac-addressvlan vlan-idip-addressinterface interface-idglobal configuration command on a routed interface, this error message appears:

Static IP source binding can only be configured on switch port.

When IP source guard with source IP filtering is enabled on an interface, DHCP snooping must be enabled on the access VLAN to which the interface belongs.

If you are enabling IP source guard on a trunk interface with multiple VLANs and DHCP snooping is enabled on all the VLANs, the source IP address filter is applied on all the VLANs.

Note If IP source guard is enabled and you enable or disable DHCP snooping on a VLAN on the trunk interface, the switch might not properly filter traffic.

When IP source guard with source IP and MAC address filtering is enabled, DHCP snooping and port security must be enabled on the interface. You must also enter the ip dhcp snooping information option global configuration command and ensure that the DHCP server supports option 82. When IP source guard is enabled with MAC address filtering, the DHCP host MAC address is not learned until the host is granted a lease. When forwarding packets from the server to the host, DHCP snooping uses the option-82 data to identify the host port.

 

 

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

 

 

 

 

 

 

OL-9775-02

 

 

22-17

 

 

 

 

 

Page 535
Image 535
Cisco Systems 3750E manual Configuring IP Source Guard, Source IP and MAC Address Filtering, 22-17