3Com 4210 9-Port - DLDP Neighbor State; Link Auto-Recovery Mechanism

1-8
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 RSY
messages and removes the corresponding neighbor
entries.
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
the local port and the neighbor is considered to be recovered to bidirectional, the port changes from
the disable state to the active state, and neighboring relationship is reestablished between the local
port and the neighbor.
Only ports in the DLDP down state can send and process recover probe packets and recover echo
packets. The auto-recovery mechanism does apply to ports that are shut down manually.