Configuring Storm Control

A traffic storm occurs when packets flood the LAN, creating excessive traffic and degrading network performance. The traffic broadcast and multicast suppression (or storm control) feature prevents LAN ports from being disrupted by a broadcast, multicast and unicast traffic storm on physical interfaces.

Prerequisites for Storm Control

  • Port-level storm control should be configured on EVC interfaces.

  • Storm control threshold value should be configured as CIR (bps, kbps, %).

  • Applicable only to broadcast, multicast and unicast packets.

Restrictions for Storm Control

  • Storm control is only enabled for ports with EVC configurations.

  • Storm control is specific to the Layer2 physical interfaces and port-channels; It is not supported on the Layer 3 interfaces or BDI.

  • Storm control is supported only for unknown unicast, broadcast, and unknown multicast ingress traffic; It is not supported for egress traffic.

  • Port-level storm control is supported on the router. EFP-level storm control is not supported.

  • Strom control on local connect and cross-connect is not supported.

Restrictions for RSP3 Module

In addition to the above, the following are applicable on the RSP3 module:

  • Storm control on port channel is not supported.

  • The BPS threshold level is 146kbps.

  • The PPS threshold level is 285pps.

  • Storm control interface statistics is not supported.

  • Storm detection does not work with jumbo frames.

  • Storm control detection is accurate with 5% deviation of configured rate.

  • Broadcast storm control is detected even when there is no EFP configured or no matching EFP under interface, and the behavior is due to hardware limitation.

Information on Storm Control

A broadcast storm occurs when huge amount of broadcast, multicast, or unknown unicast packets flood the LAN, creating excessive traffic and degrading network performance. Errors in the protocol-stack implementation or in the network configuration can also cause a storm. The mechanism to prevent and control such events is known as storm control or broadcast suppression.

Broadcast and Multicast Suppression monitors incoming traffic levels over a 1-second traffic storm control interval and, during the interval compares the traffic level with the traffic storm control level configured. The traffic storm control threshold level is a percentage of the total available bandwidth of the port. Each port has different storm control levels for broadcast, multicast, and unicast type of traffic.

Storm control uses rising and falling thresholds to block and then restore the forwarding of broadcast, unicast, or multicast packets.
  • The rising threshold is the traffic limit after which, that particular traffic is blocked.

  • The falling threshold is the traffic limit below which, that particular starts forwarding again, if it was already blocked.


Note

If a particular type of ingress traffic (unicast, broadcast and multicast) is more than the rising threshold configured on it, the interface goes to blocked state for that particular traffic.

Storm control prevents traffic on a LAN from being disrupted by a broadcast, multicast, or unicast storm on a port. Storm control is applicable for physical interfaces and is used to restrict the unicast, broadcast and multicast ingress traffic on the Layer2 interfaces. The feature is disabled by default on the Cisco ASR 903 router.

Configuring Storm Control

Before you begin

    SUMMARY STEPS

    1. enable
    2. configure terminal
    3. interface interface-id
    4. storm-control broadcast | multicast | unicast { level { rising_threshold falling_threshold | bps rising_threshold falling_threshold | pps rising_threshold falling_threshold } }
    5. storm-control action {shutdown | trap }
    6. exit

    DETAILED STEPS

      Command or Action Purpose
    Step 1

    enable

    Example:

    Router> enable

    Enables privileged EXEC mode. Enter your password if prompted.

    Step 2

    configure terminal

    Example:

    Router# configure terminal

    Enters global configuration mode.

    Step 3

    interface interface-id

    Example:

    Router# interface gigabitethernet 0/0/0

    Specifies an interface type and enters interface configuration mode.

    Step 4

    storm-control broadcast | multicast | unicast { level { rising_threshold falling_threshold | bps rising_threshold falling_threshold | pps rising_threshold falling_threshold } }

    Example:

    Router# storm-control broadcast level 1 .50

    Specifies the global broadcast, multicast, or unicast storm control suppression level as a percentage of total bandwidth.

    • broadcast —Configure broadcast storm control.

    • multicast —Configure multicast storm control.

    • unicast —Configure unknown unicast storm control.

    • level —Specifies the threshold levels for broadcast, multicast, or unicast traffic.

    • rising_threshold —Upper threshold level.

    • falling_threshold —Lower threshold level.

    • bps —Specifies the suppression level in bits per second.

    • pps —Specifies the suppression level in packets per second.

    Step 5

    storm-control action {shutdown | trap }

    Example:

    Router# storm control action trap

    Specifies the action to take when a storm occurs on a port

    • shutdown —Disables the port during a storm. The shutdown action sets the port to shut state during a storm. The port remains in shutdown state until recovered by giving a no shutdown command when the storm goes below the configured lower threshold .

    • trap —Sends an SNMP trap. The trap action generates an SNMP trap when a storm is detected . The default is to restrict the particular ingress traffic and not to send out traps.

    Step 6

    exit

    Example:

    Router# exit

    Exits interface configuration mode and returns the router to global configuration mode.

    Configuration Example

    
    
    interface GigabitEthernet0/0/1
     no ip address
     negotiation auto
     storm-control broadcast level bps 50k 40k
     storm-control multicast level pps 100 90
     storm-control unicast level 1.00 0.50
    service instance 1 ethernet
      encapsulation dot1q 2
      rewrite ingress tag pop 1 symmetric
      bridge-domain 1
    !

    Verifying Storm Control

    • Use the show storm-control command to verify the Broadcast and Multicast Suppression feature configuration.

      Router# show storm-control Gi0/15/1
      
      Interface   Type    Filter State    Upper        Lower        Current
      ---------  ------   -------------  -----------  -----------  ----------
      Gi0/0/0     Bcast    Forwarding     0 pps         0 pps       0 pps
      Gi0/0/0     Ucast    Forwarding     80.00%        20.00%      0.00%
      Gi0/0/1     Bcast    Blocking       50k bps       40k bps     0 bps
      Gi0/0/1     Mcast    Blocking       100 pps       90 pps      0 pps
      Gi0/0/1     Ucast    Blocking       1.00%         0.50%       0.00%
      
        
    • Use the show storm-control GigabitEthernet command to verify the Broadcast and Multicast Suppression feature configuration at the interface.

      Router # show storm control GigabitEthernet 0/0/1
      
      Interface   Type    Filter State   Upper        Lower        Current
      ---------  ------   -------------  -----------  -----------  ----------
      Gi0/0/1    Bcast    Blocking        50k bps      40k bps     0 bps
      Gi0/0/1    Mcast    Blocking        100 pps      90 pps      0 pps
      Gi0/0/1    Ucast    Blocking        1.00%         0.50%      0.00% 
      
      
    • Use the show run interface command to verify the action trap configured on the port.

      Router# show run interface GigabitEthernet 0/4/2
      
      Building configuration...
      Current configuration : 300 bytes
      !
      interface GigabitEthernet0/4/2
       no ip address
       negotiation auto
      storm-control broadcast level 9.00 7.00
       storm-control action trap
       service instance trunk 1 ethernet
        encapsulation dot1q 1-200
        rewrite ingress tag pop 1 symmetric
        bridge-domain from-encapsulation
       !
      end
      
    • The following example shows the action trap being sent when a storm is hit.

      Router# show storm-control G 0/4/2
      Interface   Type   Filter State   Upper        Lower        Current
      ---------  ------   -------------  -----------  -----------  ----------
      Gi0/4/2    Bcast    Blocking         9.00%        7.00%       11.00%
      May 29 14:46:28.008 IST: %STORM_CONTROL-3-TRAP: A packet storm was detected on Gi0/4/2. 
      Sending SNMP trap
      
    • The following example shows the action shutdown configured.

      Router# show run interface Gi0/4/2
      
      Building configuration...
      Current configuration : 300 bytes
      !
      interface GigabitEthernet0/4/2
       no ip address
       negotiation auto
      storm-control broadcast level 9.00 7.00
       storm-control action shutdown
       service instance trunk 1 ethernet
        encapsulation dot1q 1-200
        rewrite ingress tag pop 1 symmetric
        bridge-domain from-encapsulation
       !
      end