R3303-HP HSR6800 Routers High Availability Configuration Guide
35
second. If no Echo packet has been received from the neighbor when the Echo timer expires, the
device transits to the Disable state.
Table 12 sh
ows the relationship between the DLDP modes and neighbor entry aging.
Table 12 DLDP mode and neighbor entry aging
DLDP mode
Detecting a neighbor
after the corresponding
nei
g
hbor
entr
y
a
g
es out
Removing the neighbor
entry immediately after the
Entr
y
timer ex
p
ires
Triggering the Enhanced
timer after an Entry timer
ex
p
ires
Normal DLDP
mode
No Yes No
Enhanced
DLDP mode
Yes No Yes
Table 13 shows the relationship between DLDP modes and unidirectional link types.
Table 13 DLDP mode and unidirectional link types
Unidirectional
link type
Whether it
occurs on
fibers
Whether it
occurs on
copper twisted
p
airs
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
signals is in Disable state, and the port that does not
receive signals 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 Figure 8 mi
ght occur
(take the fiber link for example). Without DLDP enabled, the port on Router B is actually down but its state
cannot be detected by common data link protocols, so the port on Router A is still up. However, in
enhanced DLDP mode, the following occurs:
• The port on Router B is in Inactive DLDP state because it is physically down.
• The port on Router A tests the peer port on Router B after the Entry timer for the port on Router B
expires.
• The port on Router A transits to the Disable state if it receives no Echo packet from the port on Router
B when the Echo timer expires.
Figure 8 A scenario for the enhanced DLDP mode
Fiber link
GE3/0/1
(up)
GE3/0/1
(down)
Router A Router B
Unconnected or broken fiber
Ethernet
fiber port
Tx end Rx end