Cisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 4.1

Configuring IP Source Guard

This chapter describes how to configure IP Source Guard on NX-OS devices.

This chapter includes the following sections:

•Information About IP Source Guard

•Licensing Requirements for IP Source Guard

•Prerequisites for IP Source Guard

•Guidelines and Limitations

•Configuring IP Source Guard

•Verifying the IP Source Guard Configuration

•Displaying IP Source Guard Bindings

•Example Configuration for IP Source Guard

•Default Settings

•Additional References

•Feature History for IP Source Guard

Information About IP Source Guard

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 attacks that rely on 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 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 forward the packet only if the MAC address of the packet is 00:02:B3:3F:3B:99.

Virtualization Support

The following information applies to IP Source Guard used in Virtual Device Contexts (VDCs):

•IP-MAC address bindings are unique per VDC. Bindings in one VDC do not affect IP Source Guard in other VDCs.

•NX-OS does not limit binding database size on a per-VDC basis.

Licensing Requirements for IP Source Guard

The following table shows the licensing requirements for this feature:

Prerequisites for IP Source Guard

IP Source Guard has the following prerequisites:

•You should be familiar with DHCP snooping before you configure IP Source Guard.

•DHCP snooping is enabled (see the "Configuring DHCP Snooping" section on page 15-6).

Guidelines and Limitations

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.

Configuring IP Source Guard

This section includes the following topics:

•Enabling or Disabling IP Source Guard on a Layer 2 Interface

•Adding or Removing a Static IP Source Entry

Enabling or Disabling IP Source Guard on a Layer 2 Interface

You can enable or disable IP Source Guard on a Layer 2 interface.

BEFORE YOU BEGIN

By default, IP Source Guard is disabled on all interfaces.

Ensure that DHCP snooping is enabled. For more information, see the "Enabling or Disabling the DHCP Snooping Feature" section on page 15-7.

SUMMARY STEPS

1. configure terminal

2. interface ethernet slot/port

3. [no] ip verify source dhcp-snooping-vlan

4. show running-config dhcp

5. copy running-config startup-config

DETAILED STEPS

Adding or Removing a Static IP Source Entry

You can add or remove a static IP source entry on a device.

BEFORE YOU BEGIN

By default, there are no static IP source entries on a device.

SUMMARY STEPS

1. configure terminal

2. [no] ip source binding IP-address MAC-address vlan vlan-ID interface ethernet slot/port

3. show ip dhcp snooping binding [interface ethernet slot/port]

4. copy running-config startup-config

DETAILED STEPS

Verifying the IP Source Guard Configuration

To display IP Source Guard configuration information, use one of the following commands:

For detailed information about the fields in the output from these commands, see the Cisco Nexus 7000 Series NX-OS Security Command Reference, Release 4.1.

Displaying IP Source Guard Bindings

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

Example Configuration for IP Source Guard

The following example shows how to create a static IP source entry and then how to enable IP Source Guard on an interface:

ip source binding 10.5.22.17 001f.28bd.0013 vlan 100 interface ethernet 2/3

interface ethernet 2/3

  no shutdown

  ip verify source dhcp-snooping-vlan

Default Settings

Table 17-1 lists the default settings for IP Source Guard parameters.

Additional References

For additional information related to implementing IP Source Guard, see the following sections:

•Related Documents

•Standards

Related Documents

Standards

Feature History for IP Source Guard

Table 17-2 lists the release history for this feature.