Dldp Introduction; Dldp Fundamentals - H3C S5120-EI Series Operation Manual

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Figure 1-2 Unidirectional fiber link: a fiber not connected or disconnected

DLDP Introduction

Device Link Detection Protocol (DLDP) can detect the link status of a fiber cable or twisted pair. On

detecting a unidirectional link, DLDP can shut down the related port automatically or prompt users to

take measures as configured to avoid network problems.

As a data link layer protocol, DLDP cooperates with physical layer protocols to monitor the link status of

a device. While the auto-negotiation mechanism provided by the physical layer detects physical signals

and faults, DLDP performs operations such as identifying peer devices, detecting unidirectional links,

and shutting down unreachable ports. The cooperation of physical layer protocols and DLDP ensures

that physical/logical unidirectional links be detected and shut down. For a link with the devices on the

both sides of it operating properly, DLDP checks to see if the cable is connected correctly and if packets

can be exchanged between the two devices. Note that DLDP is not implemented through

auto-negotiation.

DLDP link states

A device is in one of these DLDP link states: Initial, Inactive, Active, Advertisement, Probe, Disable, and

DelayDown, as described in

Table 1-1 DLDP link states

DLDP is disabled.

DLDP is enabled but the link is down.

DLDP is enabled and the link is up, or the neighbor entries have been cleared.

All neighbors are bi-directionally reachable or DLDP has been in active state for

more than five seconds. This is a relatively state where no unidirectional link has

been detected.

DLDP enters this state if it receives a packet from an unknown neighbor. In this

state, DLDP sends packets to check whether the link is unidirectional. As soon

as DLDP transits to this state, a probe timer starts and an echo timeout timer

starts for each neighbor to be probed.

Indicates...

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