IP Source Guard (IPSG) is a security feature that restricts IP traffic on nonrouted, Layer 2 interfaces by filtering traffic based on the DHCP snooping binding database and on manually configured IP source bindings.
Your software release may not support all the features documented in
this module. For the latest caveats and feature information, see Bug Search
Tool and the release notes for your platform and 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 feature information
table at the end of this module.
Use Cisco Feature Navigator to find information about platform support
and Cisco software image support. To access Cisco Feature Navigator, go to
http://www.cisco.com/go/cfn. An account on Cisco.com is
Information About IP Source Guard
IP Source Guard
You can use IP source guard to prevent traffic attacks if a host tries to use the IP address of its neighbor and you can enable IP source guard when DHCP snooping is enabled on an untrusted interface.
After IPSG is enabled on an interface, the switch blocks all IP traffic received on the interface except for DHCP packets allowed by DHCP snooping.
The switch uses a source IP lookup table in hardware to bind IP addresses to ports. For IP and MAC filtering, a combination of source IP and source MAC lookups are used. IP traffic with a source IP address is the binding table is allowed, all other traffic is denied.
The IP source binding table has bindings that are learned by DHCP snooping or are manually configured (static IP source bindings). An entry in this table has an IP address, its associated MAC address, and its associated VLAN number. The switch uses the IP source binding table only when IP source guard is enabled.
IPSG is supported only on Layer 2 ports, including access and trunk ports. You can configure IPSG with source IP address filtering or with source IP and MAC address filtering.
IP Source Guard for Static Hosts
Do not use IPSG (IP source guard) for static hosts on uplink ports or trunk ports.
IPSG for static hosts extends the IPSG capability to non-DHCP and static environments. The previous IPSG used the entries created by DHCP snooping to validate the hosts connected to a switch. Any traffic received from a host without a valid DHCP binding entry is dropped. This security feature restricts IP traffic on nonrouted Layer 2 interfaces. It filters traffic based on the DHCP snooping binding database and on manually configured IP source bindings. The previous version of IPSG required a DHCP environment for IPSG to work.
IPSG for static hosts allows IPSG to work without DHCP. IPSG for static hosts relies on IP device tracking-table entries to install port ACLs. The switch creates static entries based on ARP requests or other IP packets to maintain the list of valid hosts for a given port. You can also specify the number of hosts allowed to send traffic to a given port. This is equivalent to port security at Layer 3.
IPSG for static hosts also supports dynamic hosts. If a dynamic host receives a
DHCP-assigned IP address that is available in the IP DHCP snooping table, the same entry is
learned by the IP device tracking table. In a stacked environment, when the master failover
occurs, the IP source guard entries for static hosts attached to member ports are retained.
When you enter the show ip device tracking all EXEC command, the
IP device tracking table displays the entries as ACTIVE.
Some IP hosts with multiple network interfaces can inject some invalid packets into a network interface. The invalid packets contain the IP or MAC address for another network interface of the host as the source address. The invalid packets can cause IPSG for static hosts to connect to the host, to learn the invalid IP or MAC address bindings, and to reject the valid bindings. Consult the vender of the corresponding operating system and the network interface to prevent the host from injecting invalid packets.
IPSG for static hosts initially learns IP or MAC bindings dynamically through an ACL-based snooping mechanism. IP or MAC bindings are learned from static hosts by ARP and IP packets. They are stored in the device tracking database. When the number of IP addresses that have been dynamically learned or statically configured on a given port reaches a maximum, the hardware drops any packet with a new IP address. To resolve hosts that have moved or gone away for any reason, IPSG for static hosts leverages IP device tracking to age out dynamically learned IP address bindings. This feature can be used with DHCP snooping. Multiple bindings are established on a port that is connected to both DHCP and static hosts. For example, bindings are stored in both the device tracking database as well as in the DHCP snooping binding database.
IP Source Guard
You can configure
static IP bindings only on nonrouted ports. If you enter the
ip source bindingmac-addressvlanvlan-id
ip-addressinterfaceinterface-id global 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 for that interface.
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.
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.
If you enable IP source guard
with source IP and MAC address filtering, 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
option-82 data to identify the host port.
When configuring IP source
guard on interfaces on which a private VLAN is configured, port security is not
You can enable
this feature when 802.1x port-based authentication is enabled.
If the number of ternary
content addressable memory (TCAM) entries exceeds the maximum, the CPU usage
When you configure
IP source guard smart logging, packets with a source address other than the
specified address or an address learned by DHCP are denied, and the packet
contents are sent to a NetFlow collector. If you configure this feature, make
sure that smart logging is globally enabled.
In a switch stack,
if IP source guard is configured on a stack member interface and you remove the
the configuration of that switch by entering the
noswitchstack-member-numberprovision global configuration command, the
interface static bindings are removed from the binding table, but they are not
removed from the running configuration. If you again provision the switch by
switchstack-member-numberprovision command, the binding is restored.
To remove the
binding from the running configuration, you must disable IP source guard before
provision command. The configuration is also removed if the
switch reloads while the interface is removed from the binding table.
(Optional) Saves your entries
in the configuration file.
Source Guard for Static Hosts on a Layer 2 Access Port
You must configure
ip device trackingmaximumlimit-number interface configuration command
globally for IPSG for static hosts to work. If you only configure this command
on a port without enabling IP device tracking globally or by setting an IP
device tracking maximum on that interface, IPSG with static hosts rejects all
the IP traffic from that interface.
This requirement also
applies to IPSG with static hosts on a private VLAN host port.
3.ip device tracking
5.switchport mode access
6.switchport access vlanvlan-id
7.ip verify source[tracking] [mac-check ]
8.ip device tracking maximumnumber
10.switchport port-security maximumvalue
Command or Action
privileged EXEC mode. Enter your password if prompted.
SwitchController# configure terminal
Enters the global
ip device tracking
SwitchController(config)# ip device tracking
Turns on the IP
host table, and globally enables IP device tracking.
Support website provides extensive online resources, including documentation
and tools for troubleshooting and resolving technical issues with Cisco
products and technologies.
security and technical information about your products, you can subscribe to
various services, such as the Product Alert Tool (accessed from Field Notices),
the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS)
most tools on the Cisco Support website requires a Cisco.com user ID and