Dldp Implementation - 3Com E4500-24 Cli Configuration Manual

Table 1-4 DLDP operating mode and neighbor entry aging
Detecting a neighbor
DLDP
after the corresponding
operating
mode
Normal
No
mode
Enhanced
Yes
mode
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
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.
Figure 1-3 A case for Enhanced DLDP mode
In normal DLDP mode, only fiber cross-connected unidirectional links (as shown in
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/processes the DLDP packets received from the peer device. DLDP packets sent in
different DLDP states are of different types.
neighbor entry ages
out
Figure 1-3
Removing the
neighbor entry
immediately after the
Entry timer expires
Yes
No
may occur, where Port B is actually down but the state of Port
Figure 1-1). The other refers to fiber pairs with one fiber not
Figure 1-2). To detect unidirectional links that are of the
1-6
Triggering the Enhanced timer
after an Entry timer expires
No
Yes (When the enhanced timer
expires, the state of the local end
is set to unidirectional link, and
the neighbor entry is aged out.)
Figure 1-1 ) can