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Whenever restarting, the GR restarter preserves all MPLS forwarding entries, marks them as stale,
1.
and starts the MPLS forwarding state holding timer for them.
After a GR helper detects that the LDP session with the GR restarter is down, it marks the FEC-label
2.
bindings learned from the session as stale and will keep these FEC-label bindings for a period of
time defined by the fault tolerant (FT) reconnect time argument. The FT reconnect time is the smaller
one between the reconnect time advertised from the peer GR restarter and the neighbor liveness
time configured locally.
During the FT reconnect time, if the LDP session fails to be re-established, the GR helper will delete
3.
the FEC-label bindings marked stale.
If the session is re-established successfully, during the LDP recovery time, the GR helper and the GR
4.
restarter will use the new LDP session to exchange the label mapping information, update the LFIB,
and delete the stale marks of the corresponding forwarding entries. The LDP recovery time is the
smaller one between the recovery time configured locally and that configured on the peer GR
restarter.
After the recovery time elapses, the GR helper deletes the FEC-label bindings that are still marked
5.
stale.
When the MPLS forwarding state holding timer expires, the GR restarter deletes the label
6.
forwarding entries that are still marked stale.
Configuration prerequisites
Before you configure LDP GR, configure MPLS LDP capability on each router that will act as the GR
restarter or a GR helper.
NOTE:
The router can act as a GR restarter or a GR helper as needed in the LDP GR process.
Configuring LDP GR
To configure LDP GR:
Step
1.
Enter system view.
2.
Enter MPLS LDP view.
3.
Enable MPLS LDP GR.
4.
Set the FT reconnect time.
5.
Set the LDP neighbor liveness
time.
6.
Set the LDP recovery time.
Gracefully restarting MPLS LDP
To test whether the MPLS LDP GR configuration has taken effect, you can perform graceful restart of MPLS
LDP. During the LDP restart process, you can see whether the packet forwarding path is changed and
whether packet forwarding is interrupted.
To restart MPLS LDP gracefully:
Command
system-view
mpls ldp
graceful-restart
graceful-restart timer reconnect
timer
graceful-restart timer
neighbor-liveness timer
graceful-restart timer recovery
timer
25
Remarks
N/A
N/A
Disabled by default
Optional
300 seconds by default
Optional
120 seconds by default
Optional
300 seconds by default
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Troubleshooting
