3Com 4500 PWR 26-Port Configuration Manual page 211

In normal DLDP mode, only fiber cross-connected unidirectional links (as shown in
can be detected.
In enhanced DLDP mode, two types of unidirectional links can be detected. One is fiber
cross-connected links (as shown in
connected or disconnected (as shown in
latter type, you need to configure the ports to operate at specific speed and in full duplex mode.
Otherwise, DLDP cannot take effect.
DLDP implementation
1) If the DLDP-enabled link is up, DLDP sends DLDP packets to the peer device, and analyzes and
processes the DLDP packets received from the peer device. DLDP in different states sends
different types of packets.
Table 17-5 Types of packets sent by DLDP
DLDP state
Active
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Probe
2) DLDP analyzes and processes received packets from the peer device as follows:
In authentication mode, DLDP authenticates the packets, and discards those failing to pass the
authentication.
DLDP processes the received DLDP packets.
Table 17-6 Process received DLDP packets
Packet type
Advertisement Extracts neighbor
packet information
Flush packet Deletes the neighbor entry from the local device
Sends echo packets
containing both
Probe packet neighbor and its own
information to the
peer
Figure 17-1). The other refers to fiber pairs with one fiber not
Figure
Advertisement packets, including those with or without an RSY tag
Advertisement packets
Probe packets
Processing procedure
If this neighbor entry does not exist on the local device,
DLDP creates the neighbor entry, enables the entry
aging timer, and switches to the probe state.
If the neighbor entry already exists on the local device,
DLDP updates the entry aging timer.
Creates the neighbor entry if this neighbor entry does
not exist on the local device.
If the neighbor entry already exists on the local device,
updates the entry aging timer.
17-6
17-2). To detect unidirectional links that are of the
Packet type
Figure 17-1 )