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Port-Level Traffic Controls

Port-based traffic control features can be used to provide protection at the port level. Catalyst switches offer Storm Control, Protected Ports, Private Virtual Local Area Network (PVLAN), Port Blocking, and Port Security features.

Storm Control

A LAN storm typically occurs when hostile packets are flooded on the LAN segment, creating unnecessary and excessive traffic resulting in network performance degradation. Several factors can cause a storm on a network; examples include errors in the protocol-stack implementation or a loophole that is exploited in a device configuration.

The Storm Control feature prevents regular network traffic from being disrupted by a broadcast, multicast, or unicast packet storm on any of the physical interfaces.

The traffic storm control (also known as a traffic suppression feature) monitors inbound packets over a 1-second interval and compares it to the configured storm-control suppression level by using one of the following methods to measure activity:

  • The percentage of total available bandwidth of the port allocated for the broadcast, multicast, or unicast traffic
  • Traffic rate over a 1-second interval in packets per second at which broadcast, multicast, or unicast packets are received on an interface

With either method, the port blocks traffic when a threshold is reached, filtering out all subsequent packets. As the port remains in a blocked state, the traffic continues to be dropped until the traffic rate drops below the suppression level, at which point the port resumes normal traffic forwarding.

To enable the traffic storm-control feature, use the storm-control {broadcast | multicast | unicast} command from the global configuration mode. By default, storm-control is disabled.

The storm-control action {shutdown | trap} command is used to specify the action to be taken when a storm is detected. By default, the storm traffic is suppressed when no action is configured.

To verify the storm-control suppression levels configured on an interface, use the show storm-control [interface] [broadcast | multicast | unicast] command.

Protected Ports (PVLAN Edge)

In some network environments, there is a requirement for no traffic to be seen or forwarded between host(s) on the same LAN segment, thereby preventing interhost communications. The PVLAN edge feature provisions this isolation by creating a firewall-like barrier, thereby blocking any unicast, broadcast, or multicast traffic among the protected ports on the switch. Note that the significance of the protected port feature is limited to the local switch, and there is no provision in the PVLAN edge feature to isolate traffic between two "protected" ports located on different switches. For this purpose, the PVLAN feature can be used. (This feature is discussed in more detail later in this chapter.)

The PVLAN edge offers the following features:

  • The switch will not forward traffic (unicast, multicast, or broadcast) between ports that are configured as protected. Data traffic must be routed via a Layer 3 device between the protected ports.
  • Control traffic, such as routing protocol updates, is an exception and will be forwarded between protected ports.
  • Forwarding behavior between a protected port and a nonprotected port proceeds normally per default behavior.

By default, no ports are configured as protected. Example 4-1 shows how to enable and verify switch ports that are configured for the protected port feature.

Example 4-1. Configuring the Protected Port Feature

Switch(config)# interface Fastethernet0/1
Switch(config-if)# switchport protected
Switch(config-if)# end

Switch# show interfaces FastEthernet 0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: static access
...
Protected: true                                    

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