24
Figure 12
LDP GR
As shown in
, 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
Configure MPLS LDP capability on each device that will act as the GR restarter or a GR helper.
NOTE:
The switch can act as a GR restarter or a GR helper as needed in the LDP GR process.
GR helper
GR helper
GR helper
GR restarter
LDP session with GR capability
