H3C S5120-EI Series Configuration Manual

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H3C S5120-EI Series Configuration Manual Manual pdf 43 page image

34performs operations such as identifying peer devices, detecting unidirectional links, and shutting downunreachable ports. The auto-negotiation mechanism and DLDP work together to make sure thatphysical/logical unidirectional links are detected and shut down, and to prevent failure of otherprotocols such as STP. If both ends of a link are operating normally at the physical layer, DLDP detectswhether the link is correctly connected at the link layer and whether the two ends can exchange packetsproperly. This is beyond the capability of the auto-negotiation mechanism at the physical layer.How DLDP worksDLDP link statesA device is in one of these DLDP link states: Initial, Inactive, Active, Advertisement, Probe, Disable, andDelayDown, as described in Table 10.Table 10 DLDP link statesState DescriptionInitial DLDP is disabled.Inactive DLDP is enabled, and the link is down.Active DLDP is enabled and the link is up, or the neighbor entries have been cleared.AdvertisementAll neighbors are bi-directionally reachable or DLDP has been in active state formore than five seconds. This is a relatively stable state where no unidirectional linkhas been detected.ProbeDLDP enters this state if it receives a packet from an unknown neighbor. In thisstate, DLDP sends packets to check whether the link is unidirectional. As soon asDLDP transits to this state, a probe timer starts and an echo timeout timer starts foreach neighbor to be probed.DisableA port enters this state when:• A unidirectional link is detected.• The contact with the neighbor in enhanced mode gets lost.• In this state, the port does not receive or send packets other than DLDPDUs.DelayDownA port in the Active, Advertisement, or Probe DLDP link state transits to this staterather than removes the corresponding neighbor entry and transits to the Inactivestate when it detects a port-down event. When a port transits to this state, theDelayDown timer is triggered.DLDP timersTable 11 DLDP timersDLDP timer DescriptionActive timerDetermines the interval for sending Advertisement packets with RSY tags, whichdefaults to 1 second. By default, a device in the active DLDP link state sends oneAdvertisement packet with RSY tags every second. The maximum number ofadvertisement packets with RSY tags that can be sent successively is 5.Advertisement timer Determines the interval for sending common advertisement packets, whichdefaults to 5 seconds.Probe timerDetermines the interval for sending Probe packets, which defaults to 1 second. Bydefault, a device in the probe state sends one Probe packet every second. Themaximum number of Probe packets that can be sent successively is 10.