H3C S5600 Series Operation Manual page 227

Operation Manual – DLDP
H3C S5600 Series Ethernet Switches
DLDP packet type
LinkDown
Recover Probe
Recover Echo
1) If the DLDP-enabled link is up, DLDP sends DLDP packets to the peer device, and
analyzes/processes the DLDP packets received from the peer device. DLDP
packets sent in different DLDP states are of different types.
Table 1-2 DLDP state and DLDP packet type
Active
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Linkdown packets are used to notify unidirectional link
emergencies (a unidirectional link emergency occurs
when the local port is down and the peer port is up).
Linkdown packets carry only the local port information
instead of the neighbor information. In some conditions, a
port is considered to be physically down if the link
connecting to the port is physically abnormal (for
example, the Rx line of the fiber on the port is
disconnected, while the Tx line operates properly). But
for the peer end, as Rx signals can still be received on the
physical layer, the port is still considered to be normal.
Such a situation is known as unidirectional link
emergency.
When a unidirectional link emergency occurs, DLDP
sends linkdown packets immediately to inform the peer of
the link abnormality. Without linkdown packets, the peer
can detect the link abnormality only after a period when
the corresponding neighbor information maintained on
the neighbor device ages out, which is three times the
advertisement interval. Upon receiving a linkdown
packet, if the peer end operates in the enhanced mode, it
enters the disable state, and sets the receiving port to the
DLDP down state (auto shutdown mode) or gives an
alarm to the user (manual shutdown mode).
Recover probe packets are used to detect whether a link
recovers to implement the port auto-recovery
mechanism. Recover probe packets carry only the local
port information instead of the neighbor information. They
request for recover echo packets as the response. A port
in the DLDP down state sends a recover probe packet
every two seconds.
Recover echo packets are response to recover probe
packets in the port auto-recovery mechanism. A link is
considered to restore to the bidirectional state if a port on
one end sends a recover probe packet, receives a
recover echo packet, and the neighbor information
contained in the recover echo packet is consistent with
that of the local port.
DLDP state
1-4
Chapter 1 DLDP Configuration
Function
Type of the DLDP packets sent
Advertisement packets, with the RSY
flag set or not set.
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