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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 12

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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Application Environment

Application Environment

This section describes the applicable environment of Loopback detection.

Using a Loopback Detection to Detect a Self-loop on an Interface

TX-RX (RX indicates the receiving end, and TX indicates the sending end) self-loops occur on an interface usually because optical fibers are connected incorrectly or the interface is damaged by high voltage. As shown in Figure 5-120, self-loops may occur on the network connected to a Switch Module interface. When a self-loop occurs, packets sent from the interface are sent back to this interface. This causes traffic forwarding errors or MAC address flapping on the interface.

Figure 5-120 Loopback detection application 1

Using a Loopback Detection to Detect a Loop on the Downstream Network

As shown in Figure 5-121, loops may occur on the network connected to a Switch Module interface. When a loop occurs, packets sent from the interface are sent back to this interface.

Figure 5-121 Loopback detection application 2

You can configure loopback detection on the interface of the Switch Module in the preceding scenarios. When a loopback is detected on the interface, the system sends an alarm. You can set the action to perform on an interface to error-down when a loopback is detected on the interface or set the time after which the interface in error-down state automatically recovers. Only users connected to the interface on which a loopback is detected and is in error-down state are affected, and other users connected to the Switch Module can still communicate.

  • Loopback detection cannot prevent loops on the entire network. It only detects loops on a single node.
  • A large number of packets are sent during loopback detection, occupying CPU resources; therefore, disable loopback detection if it is not required.
  • Loopback detection cannot be configured on an Eth-Trunk or its member interfaces.
  • You cannot enable loopback detection and STP fuction simultaneously.
Updated: 2019-08-09

Document ID: EDOC1000041694

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