Operation Manual – DLDPH3C S5600 Series Ethernet Switches Chapter 1 DLDP Configuration1-4DLDP packet type FunctionLinkDownLinkdown packets are used to notify unidirectional linkemergencies (a unidirectional link emergency occurswhen the local port is down and the peer port is up).Linkdown packets carry only the local port informationinstead of the neighbor information. In some conditions, aport is considered to be physically down if the linkconnecting to the port is physically abnormal (forexample, the Rx line of the fiber on the port isdisconnected, while the Tx line operates properly). Butfor the peer end, as Rx signals can still be received on thephysical layer, the port is still considered to be normal.Such a situation is known as unidirectional linkemergency.When a unidirectional link emergency occurs, DLDPsends linkdown packets immediately to inform the peer ofthe link abnormality. Without linkdown packets, the peercan detect the link abnormality only after a period whenthe corresponding neighbor information maintained onthe neighbor device ages out, which is three times theadvertisement interval. Upon receiving a linkdownpacket, if the peer end operates in the enhanced mode, itenters the disable state, and sets the receiving port to theDLDP down state (auto shutdown mode) or gives analarm to the user (manual shutdown mode).Recover ProbeRecover probe packets are used to detect whether a linkrecovers to implement the port auto-recoverymechanism. Recover probe packets carry only the localport information instead of the neighbor information. Theyrequest for recover echo packets as the response. A portin the DLDP down state sends a recover probe packetevery two seconds.Recover EchoRecover echo packets are response to recover probepackets in the port auto-recovery mechanism. A link isconsidered to restore to the bidirectional state if a port onone end sends a recover probe packet, receives arecover echo packet, and the neighbor informationcontained in the recover echo packet is consistent withthat of the local port.1) If the DLDP-enabled link is up, DLDP sends DLDP packets to the peer device, andanalyzes/processes the DLDP packets received from the peer device. DLDPpackets sent in different DLDP states are of different types.Table 1-2 DLDP state and DLDP packet typeDLDP state Type of the DLDP packets sentActive Advertisement packets, with the RSYflag set or not set.Advertisement Advertisement packets
