H3C Technologies H3C S6800 Series Switches - Manual (Page 33)

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LDP GR
LDP GR overview
LDP Graceful Restart (GR) enables an LSR to retain MPLS forwarding entries during an LDP restart,
ensuring continuous MPLS forwarding.
Figure 12 LDP GR
As shown in Figure 12 , GR defines the following roles:
• GR restarter—An LSR that performs GR. It must be GR-capable.
• 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
As shown in Figure 13 , LDP GR works in the following steps:
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 with the GR
restarter goes down, it performs the following operations:
GR restarter GR helper
Send label mappings
Set up an LDP session, and identify that
they are LDP GR capable
Protocol
restarts
MPLS
forwarding state
holding time
Reconnect time
LDP recovery time
Re-establish the LDP session