3Com S7906E Configuration Manual page 2195

DLDP 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 device 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
device 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 device
transits to the Disable state.
Table 1-3 DLDP mode and neighbor entry aging
Detecting a neighbor
DLDP mode corresponding
neighbor entry ages
Normal
No
DLDP mode
Enhanced
Yes
DLDP mode
The enhanced DLDP mode is designed for addressing black holes. It prevents the cases where one end
of a link is up and the other is down. If you configure the speed and the duplex mode by force on a
device, the situation shown in
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 concerning 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.
A device in the Active, Advertisement, or Probe DLDP link state transits
to DelayDown state rather than removes the corresponding neighbor
entry and transits to the Inactive state when it detects a port-down
event.
When a device transits to this state, the DelayDown timer is triggered. A
device in DelayDown state only responds to port-up events.
A device in the 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 restored.
after the Removing the neighbor
entry immediately after
the Entry timer expires
out
Yes
No
Figure 1-3 may occur, where Port B is actually down but the state of Port
1-4
Description
Triggering the Enhanced
timer after an Entry timer
No
Yes
expires