3Com S7906E Configuration Manual page 2198

Packet type
Retrieves the
Echo packet
neighbor information.
Check to see if the
Disable packet
local port is in
Disable state.
Check to see if the
RecoverProbe
local port is in
packet Disable or
Advertisement state.
Check to see if the
RecoverEcho
local port is in
packet
Disable state.
Check to see if the
LinkDown
local port operates in
packet
Enhanced mode.
3) If no echo packet is received from the neighbor, DLDP performs the following processing.
Table 1-6 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
Processing procedure
If the corresponding neighbor entry does not exist,
creates the neighbor entry, triggers the Entry timer, and
transits to Probe state.
If the neighbor information it carries
conflicts with the corresponding locally
maintained neighbor entry, drops the
The
packet.
correspondi
ng neighbor
Otherwise, sets the flag of the neighbor as
entry
two-way connected. In addition, if the
already
flags of all the neighbors are two-way
exists
connected, the device transits from Probe
state to Advertisement state and disables
the Echo timer.
If yes, no process is performed.
If not, the local port transits to Disable state.
If not, no process is performed.
If yes, returns RecoverEcho packets.
If not, no process is performed.
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.
If yes and the local port is not in Disable state, the local
transits to Disable state.
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.
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