Mpls Configuration Basics; Label Advertisement And Management - H3C S9500 Series Operation Manual

Operation Manual – MPLS Basics
H3C S9500 Series Routing Switches

1.2 MPLS Configuration Basics

Note:
Currently, the device supports the graceful restart (GR) feature of LDP. For details
about GR, refer to GR Configuration in System Volume.

1.2.1 Label Advertisement and Management

In MPLS, the decision to assign a particular label to a particular FEC is made by the
downstream LSR. The downstream LSR informs the upstream LSR of the assignment.
That is, labels are advertised in the upstream direction.
I. Label advertisement mode
Two label advertisement modes are available:
Downstream on demand (DoD): In this mode, a downstream LSR binds a label to
a particular FEC and advertises the binding only when it receives a label request
from its upstream LSR.
Downstream unsolicited (DU): In this mode, a downstream LSR does not wait for
any label request from an upstream LSR before binding a label to a particular
FEC.
An upstream LSR and its downstream LSR must use the same label advertisement
mode; otherwise, no LSP can be established normally. For more information, refer to
LDP Label
II. Label distribution control mode
There are two label distribution control modes:
Independent: In this mode, an LSR can notify label binding messages upstream
anytime. The drawback of this mode is that an LSR may have advertised to the
upstream LSR the binding of a label to a particular FEC when it receives a binding
from its downstream LSR.
Ordered: In this mode, an LSR can send label binding messages about a FEC
upstream only when it receives a specific label binding message from the next hop
for a FEC or the LSR itself is the egress node of the FEC.
III. Label retention mode
Label retention mode dictates how to process a label to FEC binding that is received by
an LSR but not useful at the moment.
There are two label retention modes:
Distribution.
Chapter 1 MPLS Basics Configuration
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