HP A5120 EI Configuration Manual page 43

DLDP mode
DLDP can operate in normal or enhanced mode.
 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 transits to the Disable state.
Table 12 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 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
occur, where the port on Device B is actually down but its state cannot be detected by common data link
protocols, so the port on Device 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.
1.
The port on Device A tests the peer port on Device B after the Entry timer for the port on Device B
2.
expires.
The port on Device A transits to the Disable state if it does not receive an Echo packet from the port
3.
on Device B when the Echo timer expires.
Figure 10 A scenario for enhanced DLDP mode
Device A
NOTE:

In normal DLDP mode, only fiber cross-connected unidirectional links can be detected.

In enhanced DLDP mode, the following types of unidirectional links can be detected: fiber cross-connected links,
and fiber pairs with one fiber or broken or not connected. When a fiber of a fiber pair is broken or not
connected, the port that can receive optical signals is in Disable state, and the other port is in Inactive state.
DLDP authentication mode
You can use DLDP authentication to prevent network attacks and illegal detection. The following DLDP
authentication modes are available.
Detecting a neighbor
after the corresponding
neighbor entry ages out
No
Yes
Port 1
(up)
Ethernet
Tx end
optical port
Fiber link
Removing the neighbor
entry immediately after
the Entry timer expires
Yes
No
Port 1
(down)
Device B
Rx end
Unconnected or broken fiber
38
Triggering the
Enhanced timer after
an Entry timer expires
No
Yes
Figure 10 may