H3C Technologies H3C S12500 Series Switches User Manual
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In normal DLDP mode, when an entry timer expires, the switch removes the corresponding neighbor
entry and sends an Advertisement packet with the RSY tag.
•
In enhanced DLDP mode, when an entry timer expires, the Enhanced timer is triggered and the
switch tests the neighbor by sending up to eight Probe packets at the frequency of one packet per
second. If no Echo packet has been received from the neighbor when the Echo timer expires, the
switch transitions to the Disable state.
Table 12 DLDP mode and neighbor entry aging
DLDP mode
Detecting a neighbor
after the corresponding
neighbor entry ages out
Removing the neighbor
entry immediately after the
Entry timer expires
Triggering the Enhanced
timer after an Entry timer
expires
Normal DLDP
mode
No Yes
No
Enhanced
DLDP mode
Yes No
Yes
Table 13 DLDP mode and unidirectional link types
Unidirectional
link type
Whether it
occurs on
fibers
Whether it
occurs on
copper twisted
pairs
In which DLDP mode unidirectional links can be
detected
Cross-connected
link
Yes
No
Both normal and enhanced modes.
Connectionless
or broken link
Yes Yes
Only enhanced mode. The port that can receive
optical signals is in Disable state, while the other port
is in Inactive state.
Enhanced DLDP mode is designed for addressing black holes. It prevents situations where one end of a
link is up and the other is down.
If you configure forced speed and full duplex mode on a port, the situation shown in
might occur
(take the fiber link for example). Without DLDP enabled, the port on Switch B is actually down but its state
cannot be detected by common data link protocols, so the port on Switch A is still up. However, in
enhanced DLDP mode, the following occurs:
The port on Device B is in Inactive DLDP state because it is physically down.
The port on Switch A tests the peer port on Switch B after the Entry timer for the port on Switch B expires.
The port on Switch A transits to the Disable state if it does not receive an Echo packet from the port on
Switch B when the Echo timer expires.
Figure 8 A scenario for enhanced DLDP mode