Configuring IP Source Guard

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.

This chapter contains the following topics:

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 in 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


Note

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 active switch 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.


Note

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 Configuration Guidelines

  • You can configure static IP bindings only on nonrouted ports. If you enter the ip source binding mac-address vlan vlan-id ip-address interface interface-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.


    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.


  • You can enable this feature when 802.1x port-based authentication is enabled.

How to Configure IP Source Guard

Enabling IP Source Guard

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Switch> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Switch# configure terminal

Enters global configuration mode.

Step 3

interface interface-id

Example:


Switch(config)# interface gigabitethernet 1/0/1

Specifies the interface to be configured, and enters interface configuration mode.

Step 4

ip verify source [mac-check ]

Example:

Switch(config-if)# ip verify source 

Enables IP source guard with source IP address filtering.

(Optional) mac-check—Enables IP Source Guard with source IP address and MAC address filtering.

Step 5

exit

Example:


Switch(config-if)# exit

Returns to global configuration mode.

Step 6

ip source binding mac-address vlan vlan-id ip-address interface interface-id

Example:


Switch(config)# ip source binding 0100.0230.0002 vlan 11 10.0.0.4 interface gigabitethernet1/0/1 

Adds a static IP source binding.

Enter this command for each static binding.

Step 7

end

Example:


Switch(config)# end

Returns to privileged EXEC mode.

Step 8

show running-config

Example:


Switch# show running-config 

Verifies your entries.

Step 9

copy running-config startup-config

Example:


Switch# copy running-config startup-config 

(Optional) Saves your entries in the configuration file.

Configuring IP Source Guard for Static Hosts on a Layer 2 Access Port

You must configure the ip device tracking maximum limit-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.

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Switch> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Switch# configure terminal

Enters global configuration mode.

Step 3

ip device tracking

Example:


Switch(config)# ip device tracking

Turns on the IP host table, and globally enables IP device tracking.

Step 4

interface interface-id

Example:


Switch(config)# interface gigabitethernet 1/0/1

Enters interface configuration mode.

Step 5

switchport mode access

Example:


Switch(config-if)# switchport mode access

Configures a port as access.

Step 6

switchport access vlan vlan-id

Example:


Switch(config-if)# switchport access vlan 10

Configures the VLAN for this port.

Step 7

ip verify source[tracking] [mac-check ]

Example:

Switch(config-if)# ip verify source tracking mac-check

Enables IP source guard with source IP address filtering.

(Optional) tracking—Enables IP source guard for static hosts.

(Optional) mac-check—Enables MAC address filtering.

The command ip verify source tracking mac-checkenables IP source guard for static hosts with MAC address filtering.
Step 8

ip device tracking maximum number

Example:


Switch(config-if)# ip device tracking maximum 8

Establishes a maximum limit for the number of static IPs that the IP device tracking table allows on the port. The range is 1to 10. The maximum number is 10.

Note 

You must configure the ip device tracking maximum limit-number interface configuration command.

Step 9

end

Example:


Switch(config)# end

Returns to privileged EXEC mode.

Monitoring IP Source Guard

Table 1. Privileged EXEC show Commands

Command

Purpose

show ip verify source [ interface interface-id ]

Displays the IP source guard configuration on the switch or on a specific interface.

show ip device tracking { all | interface interface-id | ip ip-address | mac imac-address}

Displays information about the entries in the IP device tracking table.

Table 2. Interface Configuration Commands

Command

Purpose

ip verify source tracking

Verifies the data source.

For detailed information about the fields in these displays, see the command reference for this release.

Additional References

Error Message Decoder

Description Link

To help you research and resolve system error messages in this release, use the Error Message Decoder tool.

https://www.cisco.com/cgi-bin/Support/Errordecoder/index.cgi

MIBs

MIB MIBs Link

All the supported MIBs for this release.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

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