H3C Technologies H3C S6800 Series Switches - Manual (Page 9)

1
Configuring DLDP
Overview
Unidirectional links occur when one end of a link can receive packets from the other end, but the other
end cannot receive packets sent by the first end.
Unidirectional fiber links include the following types:
• Occur when fibers are cross-connected.
• Occur when a fiber is not connected at one end or when one fiber of a fiber pair gets broken.
Figure 1 shows a correct fiber connection and the two types of unidirectional fiber connections.
Figure 1 Correct and incorrect fiber connections
Although physical layer detection mechanisms, such as the auto-negotiation mechanism, can detect
physical signals and faults, they cannot detect communication failures for unidirectional links where the
physical layer state is connected. As a data link layer protocol, the Device Link Detection Protocol (DLDP)
detects whether the fiber link or twisted-pair link is correctly connected at the link layer, and whether the
two ends can exchange packets correctly. When DLDP detects unidirectional links, it can automatically
shut down the faulty port or users can manually shut down the faulty port to avoid network problems.
DLDP cooperates with physical layer protocols to monitor link status and avoid physical and logical
unidirectional links.