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Table 12
shows the relationship between the DLDP modes and neighbor entry aging.
Table 12 DLDP mode and neighbor entry aging
Detecting a neighbor
after the corresponding
DLDP mode
neighbor entry ages
out
Normal DLDP
No
mode
Enhanced
Yes
DLDP mode
Table 13
shows the relationship between DLDP modes and unidirectional link types.
Table 13 DLDP mode and unidirectional link types
Whether it
Unidirectional
occurs on
link type
fibers
Cross-connected
Yes
link
Connectionless
Yes
or broken link
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 (take the fiber link for example). Without DLDP enabled, 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.
The port on Device A tests the peer port on Device B after the Entry timer for the port on Device B
expires.
The port on Device A transits to the Disable state if it does not receive an Echo packet from the port on
Device B when the Echo timer expires.
Figure 10 A scenario for the enhanced DLDP mode
Removing the neighbor
entry immediately after the
Entry timer expires
Yes
No
Whether it
occurs on
DLDP modes in which unidirectional links can
copper twisted
be detected
pairs
No
Both normal and enhanced modes.
Only enhanced mode.
The port that can receive signals is in Disable state,
Yes
and the port that does not receive signals is in
Inactive state.
38
Triggering the Enhanced
timer after an Entry timer
expires
No
Yes
Figure 10
may

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