Catalyst 4500 Series Switch Software Configuration Guide, 12.2(52)SG

Configuring Storm Control

This chapter describes how to configure port-based traffic control on the Catalyst 4500 series switch.

This chapter consists of these sections:

•Overview of Storm Control

•Enabling Broadcast Storm Control

•EEnabling Multicast Storm Control

•Disabling Broadcast Storm Control

•Disabling Multicast Storm Control

•Displaying Storm Control

Note For complete syntax and usage information for the switch commands used in this chapter, look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products//hw/switches/ps4324/index.html

If the command is not found inthe Catalyst 4500 Command Reference, it will be found in the larger Cisco IOS library. Refer to the Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

Overview of Storm Control

This section contains the following subsections:

•Hardware-based Storm Control Implementation

•Software-based Storm Control Implementation

Storm control prevents LAN interfaces from being disrupted by a broadcast storm. A broadcast storm occurs when broadcast packets flood the subnet, creating excessive traffic and degrading network performance. Errors in the protocol-stack implementation or in the network configuration can cause a broadcast storm.

Note Storm control and Multicast storm control are supported in hardware on all ports on the WS-X4516, WS-X4013+10GE, WS-X4516-10GE, WS-C4948, WS-C4948-10GE, and Supervisor Engine 6-E. In contrast, the supervisor engines WS-X4515, WS-X4014, and WS-X4013+ support storm control in hardware on non-blocking gigabit ports and in software on all other ports, implying that the counters for these interfaces are approximate and computed.

Hardware-based Storm Control Implementation

Broadcast suppression uses filtering that measures broadcast activity in a subnet over a one-second interval and compares the measurement with a predefined threshold. If the threshold is reached, further broadcast activity is suppressed for the duration of the interval. Broadcast suppression is disabled by default.

Figure 49-1 shows the broadcast traffic patterns on a LAN interface over a given interval. In this example, broadcast suppression occurs between times T1 and T2 and between T4 and T5. During those intervals, the amount of broadcast traffic exceeded the configured threshold.

Figure 49-1 Storm Control Example - Hardware-based Implementation

The broadcast suppression threshold numbers and the time interval combination make the broadcast suppression algorithm work with different levels of granularity. A higher threshold allows more broadcast packets to pass through.

Broadcast suppression on the Catalyst 4500 series switches (including Supervisor Engine 6-E) is implemented in hardware. The suppression circuitry monitors packets passing from a LAN interface to the switching bus. If the packet destination address is broadcast, then the broadcast suppression circuitry tracks the current count of broadcasts within the one-second interval, and when a threshold is reached, it filters out subsequent broadcast packets.

Because hardware broadcast suppression uses a bandwidth-based method to measure broadcast activity, the most significant implementation factor is setting the percentage of total available bandwidth that can be used by broadcast traffic. Because packets do not arrive at uniform intervals, the one-second interval during which broadcast activity is measured can affect the behavior of broadcast suppression.

Software-based Storm Control Implementation

When storm control is enabled on an interface, the switch monitors packets received on the interface and determines whether the packets are broadcast. The switch monitors the number of broadcast packets received within a one-second time interval. When the interface threshold is met, all incoming data traffic on the interface is dropped. This threshold is specified as a percentage of total available bandwidth that can be used by broadcast traffic. If the lower threshold is specified, all data traffic is forwarded as soon as the incoming traffic falls below that threshold.

Enabling Broadcast Storm Control

To enable storm control, perform this task:

Switch# configure terminal

Switch(config)# interface interface-id

Switch(config-if)# storm-control 
broadcast level [high level] [lower 
level]

Switch(config-if)# storm-control action 
{shutdown | trap}

Switch(config-if)# exit

Switch(config)# end

Switch# show storm-control [interface] 
broadcast

Switch# copy running-config 
startup-config

The following example shows how to enable storm control on interface.

Switch# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface fa3/1

Switch(config-if)# storm-control broadcast level 50

Switch(config-if)# end

Switch# show storm-control //Supervisor Engine 6-E

Interface  Filter State   Broadcast Multicast Level

---------  -------------  --------- --------- -----

Fi3/1      Forwarding     Enabled   Disabled  50.00% 

Switch# show int fa2/1 capabilities //Supervisor Engine 6-E

FastEthernet2/1

  Model:                 WS-X4148-RJ45V-RJ-45

  Type:                  10/100BaseTX

  Speed:                 10,100,auto

  Duplex:                half,full,auto

  Auto-MDIX:             no

  Trunk encap. type:     802.1Q

  Trunk mode:            on,off,desirable,nonegotiate

  Channel:               yes

  Broadcast suppression: percentage(0-100), hw

  Multicast suppression: percentage(0-100), hw <===== unique to Sup Engine 6-E systems

  Flowcontrol:           rx-(none),tx-(none)

  VLAN Membership:       static, dynamic

  Fast Start:            yes

  CoS rewrite:           yes

  ToS rewrite:           yes

  Inline power:          yes (Cisco Voice Protocol)

  SPAN:                  source/destination

  UDLD:                  yes

  Link Debounce:         no

  Link Debounce Time:    no

  Port Security:         yes

  Dot1x:                 yes

  Maximum MTU:           1552 bytes (Baby Giants)

  Multiple Media Types:  no

  Diagnostic Monitoring: N/A

EEnabling Multicast Storm Control

Topics include:

•Multicast Suppression on the Supervisor Engine 6-E

•Multicast Suppression on the WS-X4515, WS-X4014, and WS-X4013+ Supervisor Engines

•Multicast Suppression on all the other Supervisor Engines

Note Beginning with Cisco IOS Release 12.2(18)EW, the counters displayed with the
show interface counters storm-control command includes any multicast packets that were dropped.

Multicast Suppression on the Supervisor Engine 6-E

Supervisor Engine 6-E supports per-interface multicast suppression. This allows the user to subject incoming multicast and broadcast traffic on an interface to suppression.

Note Multicast and broadcast suppression share a common threshold per interface.
Multicast suppression takes effect only if broadcast suppression is enabled.
Disabling broadcast suppression on an interface also disables multicast suppression.

To enable multicast suppression on a Supervisor Engine 6-E, perform this task:

Switch# configure terminal

Switch(config)# interface interface-id

Switch(config-if)# storm-control 
broadcast include multicast

Switch(config-if)# exit

Switch(config)# end

Switch# show storm-control

The following example shows how to enable multicast suppression on ports that have broadcast suppression already enabled:

Switch# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# int fa3/1

Switch(config-if)# storm-control broadcast include multicast

Switch(config-if)# end

Switch#

Switch# show storm-control

Interface  Filter State   Broadcast Multicast Level

---------  -------------  --------- --------- -----

Fi3/1      Forwarding     Enabled   Enabled   50.00%

Multicast Suppression on the WS-X4515, WS-X4014, and WS-X4013+ Supervisor Engines

Hardware does not provide support for multicast suppression on the WS-X4515, WS-X4014, and WS-X4013+ supervisor engines. One consequence of using software-based broadcast suppression on these modules is that all incoming data packets are dropped. Irrespective of your selecting to configure broadcast suppression only, multicast packets are filtered as well on stub and blocking gigabit ports. The non blocking gigabit ports that do provide broadcast suppression in hardware also do not filter multicast packets.

Multicast Suppression on all the other Supervisor Engines

Multicast suppression can be enabled on a WS-X4516, WS-X4013+10GE, WS-X4516-10GE, WS-C4948, and WS-C4948-10GE supervisor engines for all ports that have storm control enabled. Multicast suppression applies to all ports that have broadcast suppression configured on them. It also applies to ports that are configured for broadcast storm-control in the future; you cannot suppress multicast traffic only.

Separate thresholds cannot be provided for broadcast and/or multicast traffic. The threshold you configure for broadcast suppression applies to both the incoming multicast traffic and broadcast traffic.

To enable multicast suppression on WS-X4516, WS-X4013+10GE, WS-X4516-10GE, and WS-C4948 supervisor engines, perform this task:

Switch# configure terminal

Switch(config)# interface interface-id

Switch(config-if)# storm-control broadcast 
include multicast

Switch(config-if)# exit

Switch(config)# end

The following example shows how to enable multicast suppression on ports that have broadcast suppression already enabled:

Switch# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# storm-control broadcast include multicast

Switch(config)# end

Switch#

Disabling Broadcast Storm Control

To disable storm control, perform this task:

Switch# configure terminal

Switch(config)# interface interface-id

Switch(config-if)# no storm-control 
broadcast level 

Switch(config-if)# no storm-control action 
{shutdown | trap}

Switch(config-if)# exit

Switch(config)# end

Switch# show storm-control broadcast 

Switch# copy running-config startup-config

The following example shows how to disable storm control on interface.

Switch# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# int fa3/1

Switch(config-if)# no storm-control broadcast level 

Switch(config-if)# end

Switch# show storm-control //Supervisor Engine 2+ to V-10GE

Interface  Filter State   Upper    Lower    Current

---------  -------------  -------  -------  -------

Switch#

Switch# show storm-control //Supervisor Engine 6-E

Interface Filter State Broadcast Multicast Level

--------- ------------- --------- --------- -----

Switch#

Disabling Multicast Storm Control

To disable multicast suppression on WS-X4516, WS-X4515, WS-X4014, and WS-X4013+ supervisor engines, perform the following task:

Switch# configure terminal

Switch(config)# interface interface-id

Switch(config-if)# [no] storm-control 
broadcast include multicast

Switch(config-if)# end

Switch(config)# end

To disable multicast suppression on the Supervisor Engine 6-E, perform this task:

Switch# configure terminal

Switch(config)# [no] storm-control 
broadcast include multicast

Switch(config-if)# no storm-control 
broadcast level

Switch(config-if)# end

Switch(config)# end

Displaying Storm Control

Note Use the show interface capabilities command to determine the mode in which storm control is supported on an interface.

The following example shows an interface that supports broadcast suppression in software (sw).

Switch# show int fa2/1 capabilities

FastEthernet2/1

  Model:                 WS-X4148-RJ45V-RJ-45

  Type:                  10/100BaseTX

  Speed:                 10,100,auto

  Duplex:                half,full,auto

  Auto-MDIX:             no

  Trunk encap. type:     802.1Q

  Trunk mode:            on,off,desirable,nonegotiate

  Channel:               yes

  Broadcast suppression: percentage(0-100), hw

  Multicast suppression: percentage(0-100), hw <=====unique to Sup Engine 6-E

  Flowcontrol:           rx-(none),tx-(none)

  VLAN Membership:       static, dynamic

  Fast Start:            yes

  CoS rewrite:           yes

  ToS rewrite:           yes

  Inline power:          yes (Cisco Voice Protocol)

  SPAN:                  source/destination

  UDLD:                  yes

  Link Debounce:         no

  Link Debounce Time:    no

  Port Security:         yes

  Dot1x:                 yes

  Maximum MTU:           1552 bytes (Baby Giants)

  Multiple Media Types:  no

  Diagnostic Monitoring: N/A

Note Use the show interfaces counters storm-control command to display a count of discarded packets.

Switch# show interfaces counters storm-control

Port         Broadcast   Multicast           Level    TotalSuppressedPackets

Fa2/1          Enabled    Disabled          10.00%              46516510

Gi3/1          Enabled     Enabled          50.00%                     0

The following example shows the output of the show storm-control command:

Switch# show storm-control //Supervisor Engine 2+ to V-10GE

Interface  Filter State   Upper    Lower    Current

---------  -------------  -------  -------  -------

Gi4/4      Forwarding       2.00%    2.00%    N/A

Switch

Note In the previous example, "current" represents the percentage of traffic suppressed at a given instant, and the value is N/A for ports that perform suppression in hardware.

Switch# show storm-control //Supervisor Engine 6-E

Interface  Filter State   Broadcast Multicast Level

---------  -------------  --------- --------- -----

Fa2/1      Blocking       Enabled   Disabled   10.00%   

Gi3/1      Link Down      Enabled   Enabled    50.00%