3Com 4500G Family Configuration Manual page 852

Packet type
Echo packet
Disable packet
RecoverProbe
packet
RecoverEcho
packet
LinkDown packet
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 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:
If the corresponding neighbor entry does not exist,
creates the neighbor entry, triggers the Entry timer, and
transits to Probe state.
Retrieves the
The
neighbor
correspondi
information.
ng neighbor
entry
already
exists
Check to see if the If yes, no process is performed.
local port is in
If not, the local port transits to Disable state.
Disable state.
Check to see if the If not, no process is performed.
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
If the neighbor information it carries
conflicts with the corresponding locally
maintained neighbor entry, drops the
packet.
Otherwise, sets the flag of the neighbor as
two-way connected. In addition, if the
flags of all the neighbors are two-way
connected, the device transits from Probe
state to Advertisement state and disables
the Echo timer.
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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