H3C Technologies H3C S7500E Series Switches - Manual (Page 48)

2-6
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DoD: In this mode, an LSR assigns a label to a FEC and distributes the FEC-label binding to its
upstream LSR only when it receives a label request from the upstream LSR.
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Currently, the S7500E series supports only the DU mode.
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An upstream LSR and its downstream LSR for an FEC must use the same label advertisement
mode; otherwise, no LSP can be established normally.
2) Label distribution control mode
There are two label distribution control modes:
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Independent: In this mode, an LSR can distribute label bindings upstream at anytime. This means
that an LSR may have distributed a label binding to its upstream LSR before it receives a binding
from its downstream LSR. As shown in
Figure 2-6 , in independent label distribution control mode,
if the label advertisement mode is DU, an LSR will assign labels to its upstream even if it has not
obtained labels from its downstream; if the label advertisement mode is DoD, the LSR distributes
a label to its upstream as long as it receives a label request from the upstream.
Figure 2-6 Independent label distribution control
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Ordered: In this mode, an LSR distributes its label binding for a FEC upstream only when it
receives a label binding for the FEC from its downstream or it is the egress of the FEC. In
Figure
2-5 , label distribution control is in ordered mode. In this case, if the label advertisement mode is
DU, an LSR will distribute a label upstream only when it receives a label binding for the FEC from
its downstream; if the label advertisement mode is DoD, after an LSR (Transit in this example)
receives a label request from its upstream (Ingress), the LSR (Transit) sends a label request to its
downstream (Egress). Then, after the LSR (Transit) receives the label binding from its
downstream (Egress), it distributes a label binding to the upstream (Ingress).