H3C Technologies H3C S12500-X Series Switches - Manual (Page 31)

23
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 6 shows a correct fiber connection and the two types of unidirectional fiber connections.
Figure 6 Correct and incorrect fiber connections
Physical layer detection mechanisms, such as auto-negotiation, 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 to avoid
network problems. Alternatively, a user can manually shut down the faulty port. DLDP cooperates with
physical layer protocols to monitor link status and avoid physical and logical unidirectional links.