Consolidated Platform Configuration Guide, Cisco IOS XE 3.3SE (Catalyst 3850 Switches)
Configuring IP Source Guard
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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:

Finding Feature Information

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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


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 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.


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.
  • 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 no switch stack-member-number provision 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 entering the switch stack-member-number provision command, the binding is restored. To remove the binding from the running configuration, you must disable IP source guard before entering the no switch provision command. The configuration is also removed if the switch reloads while the interface is removed from the binding table.

How to Configure IP Source Guard

Enabling IP Source Guard

SUMMARY STEPS

    1.    configure terminal

    2.    interface interface-id

    3.    ip verify source [mac-check ]

    4.    exit

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

    6.    end


DETAILED STEPS
      Command or Action Purpose
    Step 1 configure terminal


    Example:
    
                
              
    Switch# configure terminal
    
    
     

    Enters the global configuration mode.

     
    Step 2 interface interface-id


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

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

     
    Step 3 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 4 exit


    Example:
    Switch(config-if)# exit
    
    
     

    Returns to global configuration mode.

     
    Step 5 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 6 end


    Example:
    
                
              
    Switch(config)# end
    
    
     

    Returns to privileged EXEC mode.

     

    Enabling IP source guard with source IP and MAC filtering on VLANs 10 and 11

    Switch# configure terminal
    Enter configuration commands, one per line. End with CNTL/Z.
    Switch(config)# interface gigabitethernet 1/0/1
    Switch(config-if)# ip verify source
    Switch(config-if)# exit
    Switch(config)# ip source binding 0100.0022.0010 vlan 10 10.0.0.2 interface gigabitethernet 1/0/1
    Switch(config)# ip source binding 0100.0230.0002 vlan 11 10.0.0.4 interface gigabitethernet 1/0/1
    Switch(config)# end
    
    

    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.

    SUMMARY STEPS

      1.    configure terminal

      2.    ip device tracking

      3.    interface interface-id

      4.    switchport mode access

      5.    switchport access vlan vlan-id

      6.    ip verify source[tracking] [mac-check ]

      7.    ip device tracking maximum number

      8.    end


    DETAILED STEPS
        Command or Action Purpose
      Step 1 configure terminal


      Example:
      
                  
                
      Switch# configure terminal
      
      
       

      Enters the global configuration mode.

       
      Step 2 ip device tracking


      Example:
      Switch(config)# ip device tracking
      
      
       

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

       
      Step 3 interface interface-id


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

      Enters interface configuration mode.

       
      Step 4 switchport mode access


      Example:
      Switch(config-if)# switchport mode access
      
      
       

      Configures a port as access.

       
      Step 5 switchport access vlan vlan-id


      Example:
      Switch(config-if)# switchport access vlan 10
      
      
       

      Configures the VLAN for this port.

       
      Step 6 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 7 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 8 end


      Example:
      
                  
                
      Switch(config)# end
      
      
       

      Returns to privileged EXEC mode.

       

      Eight Examples

      This example shows how to stop IPSG with static hosts on an interface.

      Switch(config-if)# no ip verify source
      Switch(config-if)# no ip device tracking max
      
      

      This example shows how to enable IPSG with static hosts on a port.

      Switch(config)# ip device tracking
      Switch(config-if)# ip device tracking maximum 10
      Switch(config-if)# ip verify source tracking
      
      

      This example shows how to enable IPSG for static hosts with IP filters on a Layer 2 access port and to verify the valid IP bindings on the interface Gi1/0/3:

      Switch# configure terminal 
      Enter configuration commands, one per line.  End with CNTL/Z.
      Switch(config)# ip device tracking
      Switch(config)# interface gigabitethernet1/0/3
      Switch(config-if)# switchport mode access 
      Switch(config-if)# switchport access vlan 10
      Switch(config-if)# ip device tracking maximum 5
      Switch(config-if)# ip verify source tracking
      Switch(config-if)# end
      
      Switch# show ip verify source
      Interface  Filter-type  Filter-mode  IP-address       Mac-address        Vlan
      ---------  -----------  -----------  ---------------  -----------------  ----
      Gi1/0/3      ip trk       active       40.1.1.24                           10   
      Gi1/0/3      ip trk       active       40.1.1.20                           10  
      Gi1/0/3      ip trk       active       40.1.1.21                           10 
        
      

      This example shows how to enable IPSG for static hosts with IP-MAC filters on a Layer 2 access port, to verify the valid IP-MAC bindings on the interface Gi1/0/3, and to verify that the number of bindings on this interface has reached the maximum:

      Switch# configure terminal 
      Enter configuration commands, one per line.  End with CNTL/Z.
      Switch(config)# ip device tracking
      Switch(config)# interface gigabitethernet1/0/3
      Switch(config-if)# switchport mode access 
      Switch(config-if)# switchport access vlan 1
      Switch(config-if)# ip device tracking maximum 5
       
      Switch(config-if)# ip verify source tracking 
      Switch(config-if)# end
      
      Switch# show ip verify source
      Interface  Filter-type  Filter-mode  IP-address       Mac-address        Vlan
      ---------  -----------  -----------  ---------------  -----------------  ----
      Gi1/0/3      ip trk       active       deny-all                            1   
      
      

      This example displays all IP or MAC binding entries for all interfaces. The CLI displays all active as well as inactive entries. When a host is learned on a interface, the new entry is marked as active. When the same host is disconnected from that interface and connected to a different interface, a new IP or MAC binding entry displays as active as soon as the host is detected. The old entry for this host on the previous interface is marked as INACTIVE.

      Switch# show ip device tracking all 
      IP Device Tracking for wireless clients = Enabled
      Global IP Device Tracking for wired clients = Enabled
      Global IP Device Tracking Probe Count = 3
      Global IP Device Tracking Probe Interval = 30
      -----------------------------------------------------------------------------------------------
        IP Address     MAC Address   Vlan  Interface           Probe-Timeout      STATE
      -----------------------------------------------------------------------------------------------
      200.1.1.8       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.9       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.10      0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.1       0001.0600.0000  9   GigabitEthernet1/0/2                   ACTIVE
      200.1.1.1       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.2       0001.0600.0000  9   GigabitEthernet1/0/2                   ACTIVE
      200.1.1.2       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.3       0001.0600.0000  9   GigabitEthernet1/0/2                   ACTIVE
      200.1.1.3       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.4       0001.0600.0000  9   GigabitEthernet1/0/2                   ACTIVE
      200.1.1.4       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.5       0001.0600.0000  9   GigabitEthernet1/0/2                   ACTIVE
      200.1.1.5       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.6       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.7       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      
      

      This example displays all active IP or MAC binding entries for all interfaces:

      Switch# show ip device tracking all active
      IP Device Tracking for wireless clients = Enabled
      Global IP Device Tracking for wired clients = Enabled
      Global IP Device Tracking Probe Count = 3
      Global IP Device Tracking Probe Interval = 30
      -----------------------------------------------------------------------------------------------
        IP Address     MAC Address   Vlan  Interface           Probe-Timeout      STATE
      -----------------------------------------------------------------------------------------------
      200.1.1.1       0001.0600.0000  9    GigabitEthernet1/0/1                  ACTIVE
      200.1.1.2       0001.0600.0000  9    GigabitEthernet1/0/1                  ACTIVE
      200.1.1.3       0001.0600.0000  9    GigabitEthernet1/0/1                  ACTIVE
      200.1.1.4       0001.0600.0000  9    GigabitEthernet1/0/1                  ACTIVE
      200.1.1.5       0001.0600.0000  9    GigabitEthernet1/0/1                  ACTIVE
      
      

      This example displays all inactive IP or MAC binding entries for all interfaces. The host was first learned on GigabitEthernet 1/0/1 and then moved to GigabitEthernet 0/2. the IP or MAC binding entries learned on GigabitEthernet1/ 0/1 are marked as inactive.

      Switch# show ip device tracking all inactive
      IP Device Tracking for wireless clients = Enabled
      Global IP Device Tracking for wired clients= Enabled
      Global IP Device Tracking Probe Count = 3
      Global IP Device Tracking Probe Interval = 30
      -----------------------------------------------------------------------------------------------
        IP Address     MAC Address   Vlan  Interface           Probe-Timeout      STATE
      -----------------------------------------------------------------------------------------------
      200.1.1.8       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.9       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.10      0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.1       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.2       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.3       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.4       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.5       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.6       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      200.1.1.7       0001.0600.0000  8   GigabitEthernet1/0/1                   INACTIVE
      
      

      This example displays the count of all IP device tracking host entries for all interfaces:

      Switch# show ip device tracking all count
      Total IP Device Tracking Host entries: 5
      ---------------------------------------------------------------------
        Interface           Maximum Limit           Number of Entries      
      ---------------------------------------------------------------------
      Gi1/0/3                  5 
      
      

      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 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

      Technical Assistance

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