Ldp Label Distribution - 3Com MSR 50 Series Configuration Manual

1322 C 76: MPLS B
HAPTER
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LDP Label Distribution

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ASICS ONFIGURATION
A label space ID of 1 means per interface, a label space ID of 0 means per
platform.
Currently, only per platform label space is supported.
Figure 383 illustrates how LDP distribute labels.
Figure 383 Label distribution
LSP1
LSP2
Label request
Label mapping
In Figure 383, B is the upstream LSR of C on LSP1.
As described previously, there are two label advertisement modes. The main
difference between them is whether the downstream advertises the bindings
unsolicitedly or on demand.
The following details the advertisement process for each of the two modes.
DoD mode
In DoD mode, an upstream LSR sends a label request message containing the
description of a FEC to its downstream LSR, which assigns a label to the FEC,
encapsulates the binding information in a label mapping message and sends the
message back to it.
When the downstream LSR responds with label binding information depends on
the label distribution control mode used by the LSR:
In ordered mode, an LSR responds to its upstream LSR with label binding
■
information only when it receives that of its downstream LSR.
In independent mode, an LSR immediately responds to its upstream LSR with
■
label binding information no matter whether it receives that of its downstream
LSR or not.
Usually, an upstream LSR selects its downstream LSR based on the information in
its routing table. In
F on LSP2 works in independent mode.
Ingress
LSR A
LSR B
LSR E
LSR F
LER
Figure 383, all LSRs on LSP1 work in ordered mode, while LSR
Egress
LSR C
LSR D
LSR G
LSR H