H3C Technologies H3C S10500 Series Switches - Manual (Page 46)

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Packet type Processing procedure
If not, performs no processing.
LinkDown packet
Checks whether the
local port operates
in Enhanced mode
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.
In enhanced 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.
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 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:
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 relationship 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.
DLDP neighbor state
A DLDP neighbor can be in one of the three states described in Table 17 .