3com S7906E 安装指导

 

1-4 

DelayDown timer 

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. 

RecoverProbe timer 

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.  

 

DLDP can operate in two modes: normal mode and enhanced mode, as described below. 

z 

In normal DLDP mode, when an entry timer expires, the device removes the corresponding 

neighbor entry and sends an Advertisement packet with RSY tag. 

z 

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 

Normal 
DLDP mode 

No Yes 

No 

Enhanced 
DLDP mode 

Yes No 

Yes 

 

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 

 may occur, where Port B is actually down but the state of Port 

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.