R3303-HP HSR6800 Routers MPLS Configuration Guide

5
Figure 5 Label advertisement modes
As shown in Figure 5, the label advertisement modes include the DU mode and the DoD mode.
• In DU mode, an LSR assigns a label to a FEC and then distributes the FEC-label binding to its
upstream LSR without solicitation. The device supports only the DU mode.
• In DoD 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.
To establish an LSP, an upstream LSR and its downstream LSR must use the same label advertisement
mode.
Label distribution control modes include the independent mode and the ordered mode.
• In independent mode, an LSR can distribute label bindings upstream at anytime. This means that an
LSR might have distributed a label binding for a FEC to its upstream LSR before it receives a binding
for that FEC from its downstream LSR. As shown in Figure 6, in independent la
bel distribution
control mode, if the label advertisement mode is DU, an LSR assigns 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.
Egress
Transit
DU mode
DoD mode
2) Send a label request for the
FEC to the downstream.
3) Distribute a label mapping for
the FEC to the upstream upon
receiving the request.
Ingress
1) Unsolicitely distribute a label
mapping for a FEC to the upstream.
1) Send a label request for a FEC
to the downstream.
2) Unsolicitely distribute a label
mapping for the FEC to the
upstream.
4) Distribute a label mapping for
the FEC to the upstream upon
receiving the request.