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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 13

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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Introduction to DLDP

Introduction to DLDP

This section describes the definition and functions of DLDP.


The Device Link Detection Protocol (DLDP) monitors the link status of optical fibers or copper twisted pairs such as super Category 5 twisted pairs. Upon detecting a unidirectional link on an interface, DLDP automatically shuts down or prompts users to manually shut down the interface. This prevents network faults.


Sometimes unidirectional links occur on networks. On a unidirectional link, the local device can receive packets from the peer device at the link layer, but the peer device cannot receive packets from the local device. Unidirectional links result in problems such as loops on an STP topology.

As shown in Figure 11-59 and Figure 11-60, a unidirectional link fault may be caused by intersected fibers or fiber disconnection.

Figure 11-59 Intersected fibers
Figure 11-60 Fiber disconnection

As a link layer protocol, DLDP works with physical layer protocols to detect the link status. The auto negotiation mechanism at the physical layer detects physical signals and faults, and DLDP identifies the peer device, detects unidirectional links, and shuts down unreachable interfaces. The auto negotiation mechanism and DLDP work together to detect and close unidirectional links at physical and logical layers. If the interfaces on both ends of a link work properly at the physical layer, DLDP checks connections and packet exchange between the two interfaces at the link layer. This detection cannot be implemented using the auto negotiation mechanism.

Updated: 2019-12-13

Document ID: EDOC1000041694

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