How Dldp Works - HP A5830 series Configuration Manual

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 can be detected and shut down, and to prevent failure of other
protocols such as STP. If both ends of a link are operating normally at the physical layer, DLDP detects
whether the link is correctly connected at the link layer and whether the two ends can exchange packets
properly. This is beyond the capability of the auto-negotiation mechanism at the physical layer.

How DLDP works

DLDP link states
A device is in one of these DLDP link states: Initial, Inactive, Active, Advertisement, Probe, Disable, and
DelayDown, as described in
Table 10 DLDP link states
State
Initial
Inactive
Active
Advertisement
Probe
Disable
DelayDown
DLDP timers
Table 11 DLDP timers
DLDP timer
Active timer
Advertisement timer
Table 10.
Indicates...
DLDP is disabled.
DLDP is enabled, and the link is down.
DLDP is enabled and the link is up, or the neighbor entries have been cleared.
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.
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. As soon as
DLDP transits to this state, a probe timer starts and an echo timeout timer starts
for each neighbor to be probed.
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.
A port in the Active, Advertisement, or Probe DLDP link state transits to this state
rather than removes 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.
Description
Determines the interval for sending Advertisement packets with RSY tags, which
defaults 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.
Determines the interval for sending common advertisement packets, which
defaults to 5 seconds.
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