Cisco Nexus 5000 Series User manual

Configuring IP Source Guard
This chapter describes how to configure IP Source Guard on the Cisco Nexus 5000 Series switch.
This chapter includes the following sections:
•Information About IP Source Guard, page 1
•Licensing Requirements for IP Source Guard, page 2
•Prerequisites for IP Source Guard, page 2
•Guidelines and Limitations for IP Source Guard, page 2
•Default Settings for IP Source Guard, page 2
•Configuring IP Source Guard, page 3
•Displaying IP Source Guard Bindings, page 5
•Configuration Example for IP Source Guard, page 5
•Additional References for IP Source Guard, page 5
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 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.
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• 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 :
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.
Licensing Requirements for IP Source Guard
This table shows the licensing requirements for IP Source Guard.
License RequirementProduct
IP Source Guard requires no license. Any feature not
included in a license package is bundled with the
Cisco NX-OS
Cisco NX-OS system images and is provided at no
extra charge to you.
Prerequisites for IP Source Guard
Guidelines and Limitations for IP Source Guard
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.
Default Settings for IP Source Guard
This table lists the default settings for IP Source Guard parameters.
Table 1: Default IP Source Guard Parameters
DefaultParameters
Disabled on each interface.IP Source Guard
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DefaultParameters
None. No static or default IP source entries exist by
default.
IP source entries
Configuring IP Source Guard
Enabling or Disabling IP Source Guard on a Layer 2 Interface
You can enable or disable IP Source Guard on a Layer 2 interface. By default, IP Source Guard is disabled
on all interfaces.
Before You Begin
Ensure that the DHCP feature is enabled.
SUMMARY STEPS
1. configure terminal
2. interface ethernet slot/port
3. [no]ip verify source dhcp-snooping-vlan
4. (Optional) show running-config dhcp
5. (Optional) copy running-config startup-config
DETAILED STEPS
PurposeCommand or Action
Enters global configuration mode.configure terminal
Example:
switch# configure terminal
switch(config)#
Step 1
Enters interface configuration mode for the specified
interface.
interface ethernet slot/port
Example:
switch(config)# interface ethernet 2/3
switch(config-if)#
Step 2
Enables IP Source Guard on the interface. The no option
disables IP Source Guard on the interface.
[no]ip verify source dhcp-snooping-vlan
Example:
switch(config-if)# ip verify source dhcp-snooping
vlan
Step 3
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PurposeCommand or Action
(Optional)
Displays the running configuration for DHCP snooping,
including the IP Source Guard configuration.
show running-config dhcp
Example:
switch(config-if)# show running-config dhcp
Step 4
(Optional)
Copies the running configuration to the startup
configuration.
copy running-config startup-config
Example:
switch(config-if)# copy running-config
startup-config
Step 5
Adding or Removing a Static IP Source Entry
You can add or remove a static IP source entry on a device. 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. (Optional) show ip dhcp snooping binding [interface ethernet slot/port]
4. (Optional) copy running-config startup-config
DETAILED STEPS
PurposeCommand or Action
Enters global configuration mode.configure terminal
Example:
switch# configure terminal
switch(config)#
Step 1
Creates a static IP source entry for the current interface,
or if you use the no option, removes a static IP source
entry.
[no]ip source binding IP-address MAC-address vlan
vlan-ID interface ethernet slot/port
Example:
switch(config)# ip source binding 10.5.22.17
001f.28bd.0013 vlan 100 interface ethernet 2/3
Step 2
(Optional)
Displays IP-MAC address bindings for the interface
specified, including static IP source entries. Static entries
appear with the term in the Type column.
show ip dhcp snooping binding [interface ethernet slot/port]
Example:
switch(config)# show ip dhcp snooping binding
interface ethernet 2/3
Step 3
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PurposeCommand or Action
(Optional)
Copies the running configuration to the startup
configuration.
copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
Step 4
Displaying IP Source Guard Bindings
Use the show ip verify source command to display IP-MAC address bindings.
Configuration Example for IP Source Guard
This 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
Additional References for IP Source Guard
Standards
TitleStandards
—No new or modified standards are supported by this
feature, and support for existing standards has not
been modified by this feature.
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