Ldp Gr - HP HPE FlexNetwork MSR Router Series Configuration Manual

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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.

LDP GR

LDP Graceful Restart (GR) preserves label forwarding information when the signaling protocol or
control plane fails, so that LSRs can still forward packets according to forwarding entries.
Figure 12 LDP GR
As shown in
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GR restarter—An LSR that performs GR. It must be GR-capable.
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GR helper—A neighbor LSR that helps the GR restarter to complete GR.
The device can act as a GR restarter or a GR helper.
Figure 13 LDP GR operation
GR restarter
Protocol
restarts
MPLS
forwarding state
holding time
As shown in
1. LSRs establish an LDP session. The L flag of the Fault Tolerance TLV in their Initialization
messages is set to 1 to indicate that they support LDP GR.
2. When LDP restarts, the GR restarter starts the MPLS Forwarding State Holding timer, and
marks the MPLS forwarding entries as stale. When the GR helper detects that the LDP session
to the GR restarter goes down, it performs the following operations:
Figure 12, GR defines the following roles:
Set up an LDP session, and identify that
they are LDP GR capable
Re-establish the LDP session
Send label mappings
Figure 13, LDP GR operates as follows:
GR helper
Reconnect time
LDP recovery time
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