H3C Technologies H3C S3600 Series Switches - Manual (Page 227)

1-7
Packet type Processing procedure
No Discards this echo packet
No Discards this echo packet
Sets the neighbor flag bit to
bidirectional link
Echo packet
Checks
whether the
local device
is in the
probe state
Yes
Checks
whether
neighbor
information in
the packet is
the same as
that on the
local device
Yes
If all neighbors are in the
bidirectional link state, DLDP
switches from the probe state to
the advertisement state, and
sets the echo waiting timer to 0.
3) If no echo packet is received from the neighbor, DLDP performs the following processing:
Table 1-7 Processing procedure 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 waiting timer expires.
In enhanced mode, no echo packet is received
when the enhanced timer expires
DLDP switches to the disable state, outputs log
and tracking information, and sends flush
packets. Depending on the user-defined DLDP
down mode, DLDP disables the local port
automatically or prompts you to disable the port
manually. DLDP sends an RSY message and
deletes the neighbor entry.
DLDP neighbor state
A DLDP neighbor can be in one of these two states: two way and unknown. You can check the state of
a DLDP neighbor by using the display dldp command.
Table 1-8 Description on the two DLDP neighbor states
DLDP neighbor state Description
Two way The link to the neighbor operates properly.
Unknown The device is detecting the neighbor and the neighbor state is unknown.
Link Auto-recovery Mechanism
If the shutdown mode of a port is set to auto shutdown, the port is set to the DLDP down state when
DLDP detects the link connecting to the port is a unidirectional link. A port in DLDP down state does not
forward service packets or receive/send protocol packets except DLDPDUs.
A port in the DLDP down state recovers when the corresponding link recovers. A port in the DLDP down
state sends recover probe packets periodically. On receiving a correct recover echo packet (which
means that the unidirectional link is restored to a bidirectional link), it is brought up by DLDP. The
detailed process is as follows.
1) A port in the DLDP down state sends a recover probe packet every 2 seconds. Recover probe
packets carry only the local port information.
2) Upon receiving a recover probe packet, the peer end responds with a recover echo packet.
3) Upon receiving a recover echo packet, the local end checks to see if the neighbor information
carried in the recover echo packet is consistent with that of the local port. If yes, the link between