Release 15.5SY Supervisor Engine 6T Software Configuration Guide

Traffic Storm Control

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• Prerequisites for Traffic Storm Control
• Restrictions for Traffic Storm Control
• Information About Traffic Storm Control
• Default Setting for Traffic Storm Control
• How to Enable Traffic Storm Control
• Displaying Traffic Storm Control Settings

Note ● For complete syntax and usage information for the commands used in this chapter, see these publications:

http://www.cisco.com/en/US/products/ps11846/prod_command_reference_list.html

• Cisco IOS Release 15.4SY supports only Ethernet interfaces. Cisco IOS Release 15.4SY does not support any WAN features or commands.

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

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Prerequisites for Traffic Storm Control

None.

Restrictions for Traffic Storm Control

• The following LAN switching modules do not support traffic storm control:

– WS-X6148A-GE-45AF

– WS-X6148A-GE-TX

• The switch supports multicast and unicast traffic storm control on WS-X6148A-RJ-45, Gigabit Ethernet, and 10-Gigabit Ethernet LAN ports.
• The switch supports broadcast traffic storm control on all LAN ports except on those modules previously noted.
• 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-X6848-SFP-2T, WS-X6748-SFP

– WS-X6824-SFP-2T, WS-X6724-SFP

– WS-X6848-TX-2T, WS-X6748-GE-TX

– WS-X6704-10GE

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.

Information About 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.

By default, 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. These are the configurable traffic storm control optional actions:

• Shutdown—When a traffic storm occurs, traffic storm control puts the port into the error-disabled state. To reenable ports, use the error-disable detection and recovery feature or the shutdown and no shutdown commands.
• Trap—When a traffic storm occurs, traffic storm control generates an SNMP trap.

Figure 43-1 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 43-1 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 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 Setting for Traffic Storm Control

None.

How to Enable Traffic Storm Control

To enable traffic storm control, perform this task:

• You can configure traffic storm control on port channel interfaces.
• 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.

• On these modules, these levels suppress all traffic:

– WS-X6704-10GE: 0.33 percent or less

– WS-X6824-SFP-2T, WS-X6724-SFP 10Mbps ports: 0.33 percent or less

– WS-X6848-SFP-2T, WS-X6748-SFP 100Mbps ports: 0.03 percent or less

– WS-X6848-TX-2T, WS-X6748-GE-TX 100Mbps ports: 0.03 percent or less

– WS-X6816-10G-2T, WS-X6716-10G
Oversubscription Mode: 0.29 percent or less

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 example shows how the traffic storm control level configured for one mode affects all other modes that are already configured on the Gigabit Ethernet interface 4/10:

Displaying Traffic Storm Control Settings

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

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

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