HP 6125G HP 6125G & 6125G/XG Blade Switches High Availability Configur - Page 35

Configuring DLDP DLDP overview Background 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 links result in problems such as loops in an STP-enabled network. For example, the link between two switches, Switch A and Switch B, is a bidirectional link when they are connected via a fiber pair, with one fiber used for sending packets from A to B and the other for sending packets from B to A. This link is a two-way link. If one of the fibers gets broken, the link becomes a unidirectional link (one-way link). There are two types of unidirectional fiber links. One occurs when fibers are cross-connected. The other occurs when a fiber is not connected at one end, or when one fiber of a fiber pair gets broken. Figure 7 shows a correct fiber connection and the two types of unidirectional fiber connection. Figure 7 Correct and incorrect fiber connections Correct fiber conecton Device A Unidirectional connection type 1 Cross-connected fibers Device A Unidirectional connection type 2 One fiber of a fiber pair Is not connected or Is broken Device A Port 1 Port 2 Port 1 Port 2 Port 1 Port 2 Port 1 Port 2 Port 1 Port 2 Port 1 Port 2 Device B Ethernet optical port Tx end Rx end Device B Fiber link Device B Unconnected or broken fiber The Device link detection protocol (DLDP) detects unidirectional links (fiber links or twisted-pair links) and can be configured to shut down the related port automatically or prompt users to take actions to avoid network problems. As a data link layer protocol, DLDP cooperates with physical layer protocols to monitor link status. When the auto-negotiation mechanism provided by the physical layer detects physical signals and faults, DLDP 28