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Figure 9
Dynamically establishing an LSP
Label distribution and control
Label advertisement modes
Figure 10
Label advertisement modes
LDP advertises label-FEC mappings in one of the following ways:
•
Downstream Unsolicited (DU) mode
—Distributes FEC-label mappings to the upstream LSR, without
waiting for label requests. The device supports only the DU mode.
•
Downstream on Demand (DoD) mode
—Sends a label request for an FEC to the downstream LSR.
After receiving the label request, the downstream LSR distributes the FEC-label mapping for that FEC
to the upstream LSR.
NOTE:
A pair of upstream and downstream LSRs must use the same label advertisement mode. Otherwise, the
LSP cannot be established.