H3C Technologies H3C S12500 Series Switches - Manual (Page 52)

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Packet type Processing procedure
packet the local port is in
Disable state
If yes, the local port transitions to Active state if the
neighbor information the packet carries is consistent with
the local port information.
LinkDown packet
Checks whether
the local port is
operating in
Enhanced mode
If not, performs no process.
If yes and the local port is not in Disable state, sets the state
of the corresponding neighbor to unidirectional, and then
checks the state of other neighbors. If all the neighbors are
unidirectional, transitions the local port to the Disable
state. 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.
3. If no echo packet is received from the neighbor, DLDP performs the following processing.
Table 16 DLDP process 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. DLDP sets the state of the corresponding neighbor to
unidirectional, and then checks the state of other
neighbors:
• If all the neighbors are unidirectional, removes all the
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.
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 automatically sets
the state of the port where a unidirectional link is detected to DLDP down. A DLDP down port cannot
forward data traffic or send/receive any PDU 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 2 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 relationship with the neighbor.