Your software release might not support all the features documented in this module. For the latest caveats and feature information, see the Bug Search Tool at https://tools.cisco.com/bugsearch/ and the release notes for your software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "New and Changed Information"chapter or the Feature History table in this chapter.

IP Source Guard is a per-interface traffic filter that permits IP traffic only when the IP address and MAC address of each packet matches one of two sources of IP and MAC address bindings:

• Entries in the Dynamic Host Configuration Protocol (DHCP) snooping binding table.

• Static IP source entries that you configure.

Filtering on trusted IP and MAC address bindings helps prevent spoofing attacks, in which an attacker uses the IP address of a valid host to gain unauthorized network access. To circumvent IP Source Guard, an attacker would have to spoof both the IP address and the MAC address of a valid host.

You can enable IP Source Guard on Layer 2 interfaces that are not trusted by DHCP snooping. IP Source Guard supports interfaces that are configured to operate in access mode and trunk mode. When you initially enable IP Source Guard, all inbound IP traffic on the interface is blocked except for the following:

• DHCP packets, which DHCP snooping inspects and then forwards or drops, depending upon the results of inspecting the packet.

• IP traffic from static IP source entries that you have configured in the Cisco NX-OS device.

The device permits the IP traffic when DHCP snooping adds a binding table entry for the IP address and MAC address of an IP packet or when you have configured a static IP source entry.

The device drops IP packets when the IP address and MAC address of the packet do not have a binding table entry or a static IP source entry. For example, assume that the show ip dhcp snooping binding command displays the following binding table entry:

MacAddress         IpAddress    LeaseSec   Type        VLAN      Interface    
----------         ----------   ---------  ------      -------    ---------  
00:02:B3:3F:3B:99  10.5.5.2       6943    dhcp-snooping  10      Ethernet2/3

If the device receives an IP packet with an IP address of 10.5.5.2, IP Source Guard forwards the packet only if the MAC address of the packet is 00:02:B3:3F:3B:99.

IP Source Guard has the following prerequisite:

• You must enable the DHCP feature.

IP Source Guard has the following configuration guidelines and limitations:

• IP Source Guard limits IP traffic on an interface to only those sources that have an IP-MAC address binding table entry or static IP source entry. When you first enable IP Source Guard on an interface, you may experience disruption in IP traffic until the hosts on the interface receive a new IP address from a DHCP server.

• IP Source Guard is dependent upon DHCP snooping to build and maintain the IP-MAC address binding table or upon manual maintenance of static IP source entries.

This table lists the default settings for IP Source Guard parameters.

Use the show ip verify source command to display IP-MAC address bindings.

This table lists the release history for this feature.