R3303-HP HSR6800 Routers High Availability Configuration Guide

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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
performs operations such as identifying peer devices, detecting unidirectional links, and shutting down
unreachable ports.
The auto-negotiation mechanism and DLDP work together to make sure that physical/logical
unidirectional links are detected and shut down, and to prevent failure of other protocols such as STP. If
both ends of a link are operating correctly at the physical layer, DLDP detects whether the link is correctly
connected at the link layer and whether the two ends can exchange packets correctly. This is beyond the
capability of the auto-negotiation mechanism at the physical layer.
Configuring DLDP
DLDP link states
A device is in one of the following DLDP link states: Initial, Inactive, Active, Advertisement, Probe, Disable,
and DelayDown, as described in Table 10.
Table 10 DLDP link stat
es
State Indicates…
Initial 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.
Advertisement
All neighbors are bi-directionally reachable or DLDP has been in active state for
more than 5 seconds. This is a relatively stable state where no unidirectional link
has been detected.
Probe
DLDP enters this state if it receives a packet from an unknown neighbor. In this
state, DLDP sends packets to check whether the link is unidirectional. When DLDP
transits to this state, a probe timer starts and an echo timeout timer starts for each
neighbor to be probed.
Disable
A 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.
DelayDown
A port in the Active, Advertisement, or Probe DLDP link state transits to this state
rather than removing the corresponding neighbor entry and transits to the Inactive
state when it detects a port-down event. When a port transits to this state, the
DelayDown timer is triggered.
DLDP timers
Table 11 DLDP timers
DLDP timer Descri
p
tion
Active timer
Determines the interval for sending Advertisement packets with RSY tags (default is
to 1 second). By default, a device in the active DLDP link state sends one
Advertisement packet with RSY tags every second. The maximum number of
advertisement packets with RSY tags that can be sent successively is 5.