HP A5830 series Configuration Manual page 41

Packet type
LinkDown packet
If no echo packet is received from the neighbor, DLDP performs the following processing.
3.
Table 16 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
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 sets the state of the
port automatically, 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.
The port will then 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 shut down manually with the shutdown command, the auto-
recovery mechanism will not take effect.
Processing procedure
local port is in
If it is, the local port transits to Active state if the neighbor
Disable state
information the packet carries is consistent with the local port
information.
If not, performs no processing.
If yes and the local port is not in Disable state, sets the state of
the corresponding neighbor to unidirectional, and then checks
Checks whether the
the state of other neighbors. If all neighbors are
local port operates
unidirectional, transitions the local port to the Disable state. If
in Enhanced mode
the state of some neighbors is unknown, waits until the state of
these neighbors is determined. If bidirectional neighbors are
present, removes all unidirectional neighbors.
Processing procedure
DLDP sets the state of the corresponding neighbor to
unidirectional, and then checks the state of other neighbors:
•
•
•
If all neighbors are unidirectional, removes all neighbors,
transitions to the Disable state, outputs log and tracking
information, and sends Disable packets. In addition,
depending on the user-defined DLDP down mode, shuts
down the local port or prompts users to shut down the
port.
If the state of some neighbors is unknown, waits until the
state of these neighbors is determined.
If bidirectional neighbors are present, removes all
unidirectional neighbors.
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