Cisco 7600 Series Cisco IOS Software Configuration Guide, 12.2SR
Configuring Traffic Storm Control
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Configuring Traffic Storm Control

Table Of Contents

Configuring Traffic Storm Control

Understanding Traffic Storm Control

Default Traffic Storm Control Configuration

Configuration Guidelines and Restrictions

Enabling Traffic Storm Control

Displaying Traffic Storm Control Settings


Configuring Traffic Storm Control


This chapter describes how to configure the traffic storm control feature on the Cisco 7600 series routers.


Note For complete syntax and usage information for the commands used in this chapter, refer to the Cisco 7600 Series Routers Command References at this URL:

http://www.cisco.com/en/US/products/hw/routers/ps368/prod_command_reference_list.html


This chapter consists of these sections:

Understanding Traffic Storm Control

Default Traffic Storm Control Configuration

Configuration Guidelines and Restrictions

Enabling Traffic Storm Control

Understanding Traffic Storm Control

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

Traffic storm control (also called traffic 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 that you configure. The traffic storm control level is a percentage of the total available bandwidth of the port. Each port has a single traffic storm control level that is used for all types of traffic (broadcast, multicast, and unicast).

Traffic storm control monitors the level of each traffic type for which you enable traffic storm control in 1-second traffic storm control intervals. Within an interval, when the ingress traffic for which traffic storm control is enabled reaches the traffic storm control level that is configured on the port, traffic storm control drops the traffic until the traffic storm control interval ends.

Figure 39-1 shows the broadcast traffic patterns on a LAN interface over a given interval. In this example, traffic storm control occurs between times T1 and T2 and between T4 and T5. During those intervals, the amount of broadcast traffic exceeded the configured threshold.

Figure 39-1 Broadcast Suppression

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

Traffic storm control on the Cisco 7600 series routers is implemented in hardware. The traffic storm control circuitry monitors packets passing from a LAN interface to the switching bus. Using the Individual/Group bit in the packet destination address, the traffic storm control circuitry determines if the packet is unicast or broadcast, keeps track of the current count of packets within the 1-second interval, and when a threshold is reached, filters out subsequent packets.

Because hardware traffic storm control uses a bandwidth-based method to measure traffic, the most significant implementation factor is setting the percentage of total available bandwidth that can be used by controlled traffic. Because packets do not arrive at uniform intervals, the 1-second interval during which controlled traffic activity is measured can affect the behavior of traffic storm control.

The following are examples of traffic storm control behavior:

If you enable broadcast traffic storm control, and broadcast traffic exceeds the level within a 1-second traffic storm control interval, traffic storm control drops all broadcast traffic until the end of the traffic storm control interval.

If you enable broadcast and multicast traffic storm control, and the combined broadcast and multicast traffic exceeds the level within a 1-second traffic storm control interval, traffic storm control drops all broadcast and multicast traffic until the end of the traffic storm control interval.

If you enable broadcast and multicast traffic storm control, and broadcast traffic exceeds the level within a 1-second traffic storm control interval, traffic storm control drops all broadcast and multicast traffic until the end of the traffic storm control interval.

If you enable broadcast and multicast traffic storm control, and multicast traffic exceeds the level within a 1-second traffic storm control interval, traffic storm control drops all broadcast and multicast traffic until the end of the traffic storm control interval.

Default Traffic Storm Control Configuration

Traffic storm control is disabled by default.

Configuration Guidelines and Restrictions

When configuring traffic storm control, follow these guidelines and restrictions:

The following switching modules do not support unicast and multicast storm control. However, these modules support broadcast storm control:

WS-X6548-GE-TX

WS-X6548V-GE-TX

WS-X6148-GE-TX

WS-X6148V-GE-TX

WS-X6248-RJ-45

WS-X6348-RJ-45

,WS-X6148-RJ-45

WS-X6148-RJ-21

WS-X6248-RJ-21

WS-X6196-RJ-21

WS-X6148X2-RJ-45

WS-X6548-RJ-45

WS-X6548-RJ-21

The router supports broadcast traffic storm control on all LAN ports.

Except for BPDUs, traffic storm control does not differentiate between control traffic and data traffic.

When multicast suppression is enabled, traffic storm control suppresses BPDUs when the multicast suppression threshold is exceeded on these modules:

WS-X6748-SFP

WS-X6724-SFP

WS-X6748-GE-TX

WS-X6748-GE-TX

WS-X6704-10GE

WS-SUP32-GE-3B

WS-SUP32-10GE-3B

When multicast suppression is enabled on the listed modules, do not configure traffic storm control on STP-protected ports that need to receive BPDUs.

Except on the listed modules, traffic storm control does not suppress BPDUs.

Enabling Traffic Storm Control

To enable traffic storm control, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface {{type1  slot/port} | {port-channel number}}

Selects an interface to configure.

Step 2 

Router(config-if)# storm-control broadcast level level[.level]

Enables broadcast traffic storm control on the interface, configures the traffic storm control level, and applies the traffic storm control level to all traffic storm control modes enabled on the interface.

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

Disables broadcast traffic storm control on the interface.

Step 3 

Router(config-if)# storm-control multicast level level[.level]

Note The storm-control multicast command is supported only on Gigabit Ethernet interfaces.

Enables multicast traffic storm control on the interface, configures the traffic storm control level, and applies the traffic storm control level to all traffic storm control modes enabled on the interface.

Router(config-if)# no storm-control multicast level

Disables multicast traffic storm control on the interface.

Step 4 

Router(config-if)# storm-control unicast level level[.level]

Note The storm-control unicast command is supported only on Gigabit Ethernet interfaces.

Enables unicast traffic storm control on the interface, configures the traffic storm control level, and applies the traffic storm control level to all traffic storm control modes enabled on the interface.

Router(config-if)# no storm-control unicast level

Disables unicast traffic storm control on the interface.

Step 5 

Router(config-if)# end

Exits configuration mode.

Step 6 

Router# show running-config interface

Verifies the configuration.

1 type = ethernet, fastethernet, gigabitethernet, or tengigabitethernet

When configuring the traffic storm control level, note the following information:

You can configure traffic storm control on an EtherChannel (a port channel interface).

Do not configure traffic storm control on ports that are members of an EtherChannel. Configuring traffic storm control on ports that are configured as members of an EtherChannel puts the ports into a suspended state.

Specify the level as a percentage of the total interface bandwidth:

The level can be from 0 to 100.

The optional fraction of a level can be from 0 to 99.

100 percent means no traffic storm control.

0.0 percent suppresses all traffic.


Note On these modules, following levels suppress all traffic:

—WS-X6704-10GE: less than 0.33 percent round to zero
—WS-X6748-SFP: less than 0.03 percent
—WS-X6748-GE-TX: depends on speed:
if 10 Mbps: less than 0.33 percent round to zero
if 100 Mbps: less than 0.03 percent round to zero
if 1Gbps: no restriction


Because of hardware limitations and the method by which packets of different sizes are counted, the level percentage is an approximation. Depending on the sizes of the frames making up the incoming traffic, the actual enforced level might differ from the configured level by several percentage points.

This example shows how to enable multicast traffic storm control on Gigabit Ethernet interface 3/16 and how to configure the traffic storm control level at 70.5 percent. This configuration applies the traffic storm control level to all traffic storm control modes enabled on Gigabit Ethernet interface 3/16:

Router# configure terminal
Router(config)# interface gigabitethernet 3/16
Router(config-if)# storm-control multicast level 70.5
Router(config-if)# end

Displaying Traffic Storm Control Settings

To display traffic storm control information, use the commands described in Table 39-1.

Table 39-1 Commands for Displaying Traffic Storm Control Status and Configuration

Command
Purpose

Router# show interfaces [{type1  slot/port} | {port-channel number}] switchport

Displays the administrative and operational status of all Layer 2 LAN ports or the specified Layer 2 LAN port.

Router# show interfaces [{type1 slot/port} | {port-channel number}] counters storm-control

Router# show interfaces counters storm-control [module slot_number]

Displays the total number of packets discarded for all three traffic storm control modes, on all interfaces or on the specified interface.

1 type = ethernet, fastethernet, gigabitethernet, or tengigabitethernet



Note The show interfaces [{interface_type slot/port} | {port-channel number}] counters command does not display the discard count. You must the storm-control keyword to display the discard count.