H3C Technologies H3C SR8800 - Manual (Page 36)

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1. Whenever restarting, the GR restarter preserves all MPLS forwarding entries, marks them as stale,
and starts the MPLS forwarding state holding timer for them.
2. After a GR helper detects that the LDP session with the GR restarter is down, it marks the FEC-label
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.
3. During the FT reconnect time, if the LDP session fails to be re-established, the GR helper will delete
the FEC-label bindings marked stale.
4. If the session is re-established successfully, during the LDP recovery time, the GR helper and the GR
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.
5. After the recovery time elapses, the GR helper deletes the FEC-label bindings that are still marked
stale.
6. When the MPLS forwarding state holding timer expires, the GR restarter deletes the label
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 Command Remarks
1. Enter system view. system-view N/A
2. Enter MPLS LDP view. mpls ldp N/A
3. Enable MPLS LDP GR. graceful-restart Disabled by default
4. Set the FT reconnect time.
graceful-restart timer reconnect
timer
Optional
300 seconds by default
5. Set the LDP neighbor liveness
time. graceful-restart timer
neighbor-liveness timer Optional
120 seconds by default
6. Set the LDP recovery time.
graceful-restart timer recovery
timer Optional
300 seconds by default
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: