Configuring Port-Based Traffic Control

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

Note For complete syntax and usage information for the switch commands used in this chapter, refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/index.htm.

This chapter consists of these sections:

•Overview of Storm Control

•Enabling Storm Control

•Disabling Storm Control

•Displaying Storm Control

•Multicast Storm Control

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 is supported in hardware on all ports on the WS-X4516 supervisor engine. 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. Multicast storm control is only supported on the WS-X4516 supervisor engine.

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 38-1 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 38-1 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 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 or not 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 Storm Control

To enable storm control, perform this task:

 
Command
Purpose

Step 1  

Switch# configure terminal

Enters global configuration mode.

Step 2  

Switch(config)# interface interface-id

Enters interface configuration mode and enter the port to configure.

Step 3  

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

Configures broadcast storm control.

Specifies the upper threshold levels for broadcast traffic. The storm control action occurs when traffic utilization reaches this level.

(Optional) Specifies the falling threshold level. The normal transmission restarts (if the action is filtering) when traffic drops below this level for interfaces that support software-based suppression.

Note For ports that perform hardware-based suppression, the lower threshold is ignored.

Step 4  

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

Specifies the action to be taken when a storm is detected.

The default is to filter out the broadcast traffic and not to send out traps.

The shutdown keyword sets the port to error-disable state during a storm. If the recover interval is not set, the port remains in shutdown state.

Note The trap keyword generates an SNMP trap when a storm is detected. This keyword is available but not supported in the
12.1(19)EW release.

Step 5  

Switch(config-if)# exit

Returns to configuration mode.

Step 6  

Switch(config)# end

Returns to privileged EXEC mode.

Step 7  

Switch# show storm-control [interface] 
broadcast

Displays the number of packets suppressed.

Step 8  

Switch# copy running-config 
startup-config

(Optional) Saves your entries in the configuration file.

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

Switch# conf t

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

Switch(config)# int fa3/1

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

Switch(config-if)# end

Switch# write memory

Building configuration...


00:11:06: %SYS-5-CONFIG_I: Configured from console by consoleCompressed configuration from 
5394 bytes to 1623 bytes[OK]

Switch#sh  stor

Switch#sh  storm-control 

Interface  Filter State   Upper    Lower    Current

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

Fa3/1      Forwarding      50.00%   50.00%    0.00%

Switch#

Disabling Storm Control

To disable storm control, perform this task:

 
Command
Purpose

Step 1  

Switch# configure terminal

Enters global configuration mode.

Step 2  

Switch(config)# interface 
interface-id

Enters interface configuration mode and enter the port to configure.

Step 3  

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

Disables port storm control.

Step 4  

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

Disables the specified storm control action and returns to default filter action.

Step 5  

Switch(config-if)# exit

Returns to configuration mode.

Step 6  

Switch(config)# end

Returns to privileged EXEC mode.

Step 7  

Switch# show storm-control 
broadcast

Verifies your entries.

Step 8  

Switch# copy running-config 
startup-config

(Optional) Saves your entries in the configuration file.

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

Switch# conf t

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# wr

Building configuration...


00:12:09: %SYS-5-CONFIG_I: Configured from console by consoleCompressed configuration from 
5357 bytes to 1594 bytes[OK]

Switch# sh sto

Switch# sh storm-control 

Interface  Filter State   Upper    Lower    Current

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

Switch#

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 interfaces g4/4 capabilities

show interfaces g4/4 capabilities

GigabitEthernet4/4

  Model:                 WS-X4418-Gbic

  Type:                  1000BaseSX

  Speed:                 1000

  Duplex:                full

  Trunk encap. type:     802.1Q

  Trunk mode:            on,off,desirable,nonegotiate

  Channel:               yes

  Broadcast suppression: percentage(0-100), sw 

  Flowcontrol:           rx-(off,on,desired),tx-(off,on,desired)

  VLAN Membership:       static, dynamic

  Fast Start:            yes

  Queuing:               rx-(N/A), tx-(4q1t, Shaping)

  CoS rewrite:           yes

  ToS rewrite:           yes

  Inline power:          no

  SPAN:                  source/destination

  UDLD:                  yes

  Link Debounce:         no

  Link Debounce Time:    no

  Port Security:         yes

  Dot1x:                 yes

  Maximum MTU:           1552 bytes (Baby Giants)

  Media Type:            no


Switch#

The following example shows an interface that supports broadcast suppression in hardware (hw). 

Switch# show interfaces g4/1 capabilities

show interfaces g4/1 capabilities

GigabitEthernet4/1

  Model:                 WS-X4418-Gbic

  Type:                  No Gbic

  Speed:                 1000

  Duplex:                full

  Trunk encap. type:     802.1Q,ISL

  Trunk mode:            on,off,desirable,nonegotiate

  Channel:               yes

  Broadcast suppression: percentage(0-100), hw 

  Flowcontrol:           rx-(off,on,desired),tx-(off,on,desired)

  VLAN Membership:       static, dynamic

  Fast Start:            yes

  Queuing:               rx-(N/A), tx-(4q1t, Sharing/Shaping)

  CoS rewrite:           yes

  ToS rewrite:           yes

  Inline power:          no

  SPAN:                  source/destination

  UDLD:                  yes

  Link Debounce:         no

  Link Debounce Time:    no

  Port Security:         yes

  Dot1x:                 yes

  Maximum MTU:           1552 bytes (Baby Giants)

  Media Type:            no


Switch#

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

Switch# show interfaces counters storm-control


Port        BcastSuppLevel    TotalSuppressedPackets

Gi4/4                2.00%                     0

Switch#

Note Use the show storm-control command to display the configured thresholds and status of storm on an interface. 

Switch# show storm-control


Interface  Filter State   Upper    Lower    Current

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

Gi4/4      Forwarding       2.00%    2.00%    N/A

Switch

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

Multicast Storm Control

When a large amount of broadcast (and/or multicast) packets congest a network, the event is referred to as a broadcast storm. A LAN broadcast storm affects network performance and could paralyze the whole network.

Note Multicast storm control is available only on WS-X4516 supervisors; only a hardware-based solution is provided.

Multicast Suppression on the WS-X4516 Supervisor Engine

Multicast suppression can be enabled on a WS-X4516 supervisor engine 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 will be configured for broadcast storm-control in the future; you cannot suppress multicast traffic only. Beginning in Release 12.2(18)EW, the counters displayed with the show interface counters storm-control command will include any multicast packets that were dropped.

You cannot provide separate thresholds for broadcast and/or multicast traffic. The threshold you configure for broadcast suppression applies to both the incoming multicast traffic and broadcast traffic. Moreover, the configuration is common and must be set for each interface.

To enable multicast suppression, perform this task:

 
Command
Purpose

Step 1  

Switch# configure terminal

Enters global configuration mode.

Step 2  

Switch(config)# interface 
interface-id

Enters interface configuration mode and enter the port to configure.

Step 3  

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

Enable multicast suppression.

Step 4  

Switch(config-if)# end

Returns to privileged EXEC mode.

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

Switch# configuration terminal

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

Switch(config)# interface fa3/1

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

Switch(config-if)# end

Switch#

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.