H3C S3100-52P Operation Manual page 221

Operation Manual – DLDP
H3C S3100-52P Ethernet Switch
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
DLDP state
Active
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Probe
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.
Type of the DLDP packets sent
Advertisement packets, with the RSY flag set or not set.
Advertisement packets
Probe packets
1-4
Chapter 1 DLDP Configuration
Function