Overview 185
DLDP Fundamentals 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 30.
DLDP timers
Table 30 DLDP link states
State Description
Initial This state indicates that DLDP is not enabled.
Inactive This state indicates that DLDP is enabled but the link is down.
Active This state indicates that:
■ DLDP is enabled and the link is up.
■ The neighbor entries are cleared.
Advertisement This state indicates that a device can communicate normally with all its
neighbors in both directions or DLDP remains in active state for more than five
seconds. It is the normal state where no unidirectional link is detected.
Probe A device enters this state if it receives a packet from an unknown neighbor. In
this state, DLDP sends packets to check whether the link is a unidirectional
link. After a device enters this state, the probe sending timer is triggered, and
an echo waiting timer is triggered for each neighbor to be detected.
Disable A device enters this state when:
■ A unidirectional link is detected.
■ The contact with a neighbor in enhanced mode gets lost.
In this state, no DLDP packet is sent or accepted.
DelayDown A device in the Active, Advertisement, or Probe DLDP link state transits to this
state rather than remove the corresponding neighbor entry and transits to the
Inactive state when it detects a port-down event. When a device transits to
this state, the DelayDown timer is triggered.
Table 31 DLDP timers
DLDP timer Description
Active timer Determines the Interval to send Advertisement packets with RSY tag,
which defaults to 1 second.
When a device transits to the active DLDP link state, it sends
Advertisement packets with RSY tag according to this timer. The
maximum number of this type of packets that can be sent successively is
5.
Advertisement timer Determines the interval to send advertisement packets, which defaults
to 5 seconds.
Probe timer Determines the interval to send Probe packets, which defaults to 0.5
seconds. The maximum number of this type of packets that can be sent
successively is 10.
Echo timer This timer is set to 10 seconds and is triggered when a device transits to
the Probe state or an enhanced detect is launched. When the Echo
waiting timer expires and no Echo packet is received from a neighbor
device, the link is set as a unidirectional link and the device transits to
the Disable state. In this case, the device sends Disable packets, prompts
the user to shut down the port or shuts down the port automatically
(depending on the DLDP down mode configured), and removes the
corresponding neighbor entries.
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