3Com Switch 7750 Configuration Guide Guide

200 CHAPTER 26: DLDP CONFIGURATION
Figure 50 Fiber which is not connected or disconnected
DLDP provides the following features:
■ As a link layer protocol, it works together with the physical layer protocols to
monitor the link status of a device.
■ While the auto-negotiation mechanism on the physical layer detects physical
signals and faults; DLDP identifies peer devices and unidirectional links, and
disables unreachable ports.
■ Even if the links of both ends can normally operate individually on the physical
layer, DLDP can detect (at the link layer) whether these links are connected
correctly and packets can be exchanged normally between the two ends. This
detection cannot be implemented by the auto-negotiation mechanism.
DLDP Fundamentals DLDP status
DLDP may be in one of the seven states: initial, inactive, active, advertisement,
probe, disable, and delaydown.
SwitchB
SwitchA
PC
GE2/0/3
GE2/0/3
GE2/0/4
GE2/0/4
SwitchB
SwitchA
PC
GE2/0/3
GE2/0/3
GE2/0/4
GE2/0/4
Tabl e 127 DLDP status
Status Description
Initial DLDP is not enabled.
Inactive DLDP is enabled but the corresponding link is down
Active
DLDP is enabled and the link is up, or the state within five seconds after
an neighbor entry is cleared
Advertisement
All neighbors communicate normally in both direction, or DLDP
remains in active status for more than five seconds and enters this
status. It is a stable status when no unidirectional link is found
Probe
DLDP sends packets to check if it is a unidirectional link. It enables the
probe sending timer and an echo waiting timer for each target
neighbor.
Disable
DLDP detects a unidirectional link, or finds (in enhanced mode) that a
neighbor ages. In this case, DLDP does not receive or send DLDP
packets.