4-8
Packet type
Processing procedure
packet
local port is in
Disable or
Advertisement state
If yes, returns RecoverEcho packets.
If not, no process is performed.
RecoverEcho
packet
Checks whether the
local port is in
Disable state
If yes, the local port transits to Active state if the neighbor
information the packet carries is consistent with the local port
information.
If not, no process is performed.
LinkDown packet
Checks whether the
local port operates
in Enhanced mode
If yes and the local port is not in Disable state, the local port
transits to Disable state.
3) If no echo packet is received from the neighbor, DLDP performs the following processing.
Table 4-6
Processing procedure when no echo packet is received from the neighbor
No echo packet received from the neighbor
Processing procedure
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.
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.
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 where a unidirectional link is detected to DLDP down automatically. 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 as follows:
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
neighborship 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.
