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Configuration Guide - Ethernet Switching

CloudEngine 8800, 7800, 6800, and 5800 V200R003C00

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, MUX VLAN, Voice VLAN, VLAN mapping, QinQ, GVRP, VCMP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, and Layer 2 protocol transparent transmission.
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Application Scenarios for Loopback Detection

Application Scenarios for 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 13-1, self-loops may occur on the network connected to a Switch 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 13-1 Loopback detection application 1

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

As shown in Figure 13-2, loops may occur on the network connected to a Switch interface. When a loop occurs, packets sent from the interface are sent back to this interface.

Figure 13-2 Loopback detection application 2

You can configure loopback detection on the interface of the Switch 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 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 used with ring network technologies including ERPS, RRPP, SEP, Smart Link, STP, RSTP, MSTP, and VBST. Do not configure ring network technologies on an interface of the LBDT-enabled VLAN. If LBDT has been enabled globally and a ring network technology need to be configured on an interface, disable LBDT on that interface first.
Updated: 2019-05-08

Document ID: EDOC1100004351

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