41
Table 15 DLDP process when no echo packet is received from the neighbor
No echo packet received from the
neighbor
In normal mode, no echo packet is received
when the Echo timer expires.
DLDP transits to the Disable state, outputs log and tracking
information, and sends Disable packets. In addition,
depending on the user-defined DLDP down mode, DLDP
shuts down the local port or prompts users to shut down
the port, and removes the corresponding neighbor entry.
In enhanced mode, no echo packet is received
when the Echo timer expires.
Link auto-recovery mechanism
If the port shutdown mode upon detection of a unidirectional link is set to auto, DLDP automatically sets
the state of the port, where a unidirectional link is detected, to DLDP down. A DLDP down port cannot
forward data traffic or send/receive any PDUs except DLDPDUs.
On a DLDP down port, DLDP monitors the unidirectional link. Once DLDP finds out that the state of the
link has restored to bidirectional, it brings up the port. The specific process is:
The DLDP down port sends out a RecoverProbe packet, which carries only information about the local
port, every two seconds. Upon receiving the RecoverProbe packet, the remote end returns a RecoverEcho
packet. Upon receiving the RecoverEcho packet, the local port checks whether neighbor information in the
RecoverEcho packet is the same as the local port information. If they are the same, the link between the
local port and the neighbor is considered to have been restored to a bidirectional link, and the port will
transit from Disable state to Active state and re-establish relationship with the neighbor.
Only DLDP down ports can send and process Recover packets, including RecoverProbe packets and
RecoverEcho packets. If related ports are manually shut down with the shutdown command, the auto-
recovery mechanism will not take effect.
DLDP neighbor state
A DLDP neighbor can be in one of the three states described in Table 16.
Table 16 Description on DLDP neighbor states
A neighbor is in this state when it is just detected and is being probed. A
neighbor is in this state only when it is being probed. It transits to Two way
state or Unidirectional state after the probe operation finishes.
A neighbor is in this state after it receives response from its peer. This state
indicates the link is a two-way link.
A neighbor is in this state when the link connecting it is detected to be a
unidirectional link. After a switch transits to this state, the corresponding
neighbor entries maintained on other devices are removed.
DLDP configuration task list
Complete the following tasks to configure DLDP:
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