H3C Technologies H3C S7500E Series Switches - Manual (Page 69)

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Figure 2-12 LDP GR
As shown in Figure 2-12 , two LDP peers perform GR negotiation when establishing an LDP session.
The LDP session established is GR capable only when both peers support LDP GR.
The working procedure of LDP GR is as follows:
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 configuring LDP GR, complete the following task:
z
Configuring MPLS LDP capability on each device to be the GR restarter or a GR helper.