1-2Figure 1-2 Fiber correct connection/disconnection in one directionGE1/0/10 SwitchA GE1/0/11GE1/0/10 SwitchB GE1/0/11PCDLDP provides the following features:z As a link layer protocol, it works together with the physical layer protocols to monitor the link statusof a device. While the auto-negotiation mechanism on the physical layer detects physical signalsand faults; DLDP identifies peer devices and unidirectional links, and disables unreachable ports.z Even if the links of both ends can normally operate individually on the physical layer, DLDP candetect (at the link layer) whether these links are connected correctly and packets can beexchanged normally between the two ends. This detection cannot be implemented by theauto-negotiation mechanism.z When the port works in mandatory full duplex mode and the mandatory rate, DLDP can detect fiberdisconnection in one direction as shown in Figure 1-2.z When the port works in auto-negotiation duplex mode and auto-negotiation rate, even if DLDP isenabled, it does not take effect when fiber in one direction is disconnected as shown in Figure 1-2,in that case, it considers that the port is down.DLDP FundamentalsDLDP statusA link can be in one of these DLDP states: initial, inactive, active, advertisement, probe, disable, anddelaydown.Table 1-1 DLDP statusStatus DescriptionInitial DLDP is not enabled.Inactive DLDP is enabled but the corresponding link is downActive DLDP is enabled and the link is up, or an neighbor entry is clearedAdvertisementAll neighbors communicate normally in both direction, or DLDPremains in active status for more than five seconds and enters thisstatus. It is a stable status when no unidirectional link is found
