3Com 4510G Configuration Manual page 812

Packet type
RecoverProbe
packet
RecoverEcho
packet
LinkDown packet
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
In normal mode, no echo packet is
received when the Echo timer expires.
In enhanced mode, no echo packet is
received when the enhanced 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 where a unidirectional link is detected to DLDP down automatically. A DLDP down port cannot
forward service 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. The auto-recovery mechanism does not take effect on ports manually shut
down.
DLDP neighbor state
A DLDP neighbor can be in one of the three states described in
If not, no process is performed.
Check to see if the
local port is in
Disable or
If yes, returns RecoverEcho packets.
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state.
If not, no process is performed.
Check to see if the
If yes, the local port transits to Active state if the neighbor
local port is in
information the packet carries is consistent with the local
Disable state.
port information.
If not, no process is performed.
Check to see if the
local port operates
in Enhanced
If yes and the local port is not in Disable state, the local
mode.
transits to Disable state.
Processing procedure
Processing procedure
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.
Table
4-7
4-7.