R2511-HP MSR Router Series MPLS Configuration Guide(V5)

Figure 12 LDP GR

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.

LDP GR works in the following procedure:

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 keeps 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 deletes 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 uses 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

Configure MPLS LDP capability on each device acting as the GR restarter or a GR helper. (The device can

act as a GR restarter or a GR helper as needed in the LDP GR process.)

Configuration procedure

To configure LDP GR:

GR helper

GR helper GR helper

GR restarter

LDP session with GR capability