H3C S9500E Series Configuration Manual page 34

DLDP timer
Enhanced timer
DelayDown timer
RecoverProbe timer
DLDP mode
DLDP can operate in two modes: normal mode and enhanced mode, as described below.
•
In normal DLDP mode, when an entry timer expires, the switch removes the corresponding
neighbor entry and sends an Advertisement packet with RSY tag.
•
In enhanced DLDP mode, when an entry timer expires, the Enhanced timer is triggered and
the switch sends up to eight Probe packets at a frequency of one packet per second to test
the neighbor. If no Echo packet is received from the neighbor when the Echo timer expires,
the switch transits to the Disable state.
Table 11 DLDP mode and neighbor entry aging
DLDP mode
Normal DLDP
mode
Enhanced DLDP
mode
Enhanced DLDP mode is designed for addressing black holes. It prevents cases where one end of
a link is up and the other is down. If you configure a switch's speed and the duplex mode by
force, the situation shown in Figure 5 may occur, where Port B is actually down but the state of
Port B cannot be detected by common data link protocols, so Port A is still up. In enhanced DLDP
mode, however, Port A tests Port B after the Entry timer for Port B expires. Port A then transits to
the Disable state if it receives no Echo packet from Port A when the Echo timer expires. As Port B
is physically down, it is in the Inactive DLDP state.
Description
In the enhanced mode, this timer is triggered if no packet is received from a neighbor
when the entry aging timer expires. Enhanced timer is set to 1 second.
After the Enhanced timer is triggered, the switch sends up to eight probe packets to
the neighbor at a frequency of one packet per second.
A switch in the Active, Advertisement, or Probe DLDP link state transits to DelayDown
state rather than remove the corresponding neighbor entry, and transits to the
Inactive state when it detects a port-down event.
When a switch transits to this state, the DelayDown timer is triggered. A switch in
DelayDown state only responds to port-up events.
A switch in DelayDown state resumes its original DLDP state if it detects a port-up
event before the DelayDown timer expires. Otherwise, it removes the corresponding
DLDP neighbor information and transits to the Inactive state.
This timer is set to 2 seconds. That is, a port in the Disable state sends one
RecoverProbe packet every two seconds to detect whether a unidirectional link has
been restored to bidirectional.
Detecting a neighbor
after the corresponding
neighbor entry ages out
No
Yes
34
Removing the neighbor
entry immediately after the
Entry timer expires
Yes
No
Triggering the
Enhanced timer after
an Entry timer expires
No
Yes