HP FlexNetwork 10500 Series Configuration Manual page 29

NOTE:
To successfully establish an LSP, a pair of upstream and downstream LSRs must use the same
label advertisement mode.
Label distribution control
LDP controls label distribution in one of the following ways:
•
Independent label distribution—Distributes an FEC-label mapping to an upstream LSR at
any time. An LSR might distribute a mapping for an FEC to its upstream LSR before it receives
a label mapping for that FEC from its downstream LSR. As shown in
each LSR distributes a label mapping for an FEC to its upstream LSR whenever it is ready to
label-switch the FEC. The LSRs do not need to wait for a label mapping for the FEC from its
downstream LSR. In DoD mode, an LSR distributes a label mapping for an FEC to its upstream
LSR after it receives a label request for the FEC. The LSR does not need to wait for a label
mapping for the FEC from its downstream LSR.
Figure 11 Independent label distribution control mode
DU mode
DoD mode
•
Ordered label distribution—Distributes a label mapping for an FEC to its upstream LSR only
after it receives a label mapping for that FEC from its downstream LSR unless the local node is
the egress node of the FEC. As shown in
mapping for an FEC to its upstream LSR only if it receives a label mapping for the FEC from its
downstream LSR. In DoD mode, when an LSR (Transit) receives a label request for an FEC
from its upstream LSR (Ingress), it continues to send a label request for the FEC to its
downstream LSR (Egress). After the transit LSR receives a label mapping for the FEC from the
egress LSR, it distributes a label mapping for the FEC to the ingress LSR.
Label retention mode
The label retention mode specifies whether an LSR maintains a label mapping for an FEC learned
from a neighbor that is not its next hop.
•
Liberal label retention—Retains a received label mapping for an FEC regardless of whether
the advertising LSR is the next hop of the FEC. This mechanism allows for quicker adaptation to
topology changes, but it wastes system resources because LDP has to keep useless labels.
The device only supports liberal label retention.
•
Conservative label retention—Retains a received label mapping for an FEC only when the
advertising LSR is the next hop of the FEC. This mechanism saves label resources, but it
cannot quickly adapt to topology changes.
Unsolicitedly distributes a label
mapping for a FEC to the upstream.
Ingress
1) Sends a label request for a
FEC to the downstream.
2) Distributes a label mapping for
the FEC to the upstream upon
receiving the request.
Unsolicitedly distributes a label
mapping for a FEC to the upstream.
Transit
1) Sends a label request for a
FEC to the downstream.
2) Distributes a label mapping for
the FEC to the upstream upon
receiving the request.
Figure 10, in DU mode, an LSR distributes a label
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Figure 11, in DU mode,
Egress