Control Plane Failure - Cisco ASR 9000 Series Configuration Manual

Implementing MPLS Label Distribution Protocol

Control Plane Failure

When a control plane failure occurs, connectivity can be affected. The forwarding states installed by the router
control planes are lost, and the in-transit packets could be dropped, thus breaking NSF.
This figure illustrates a control plane failure and shows the process and results of a control plane failure leading
to loss of connectivity.
Figure 4: Control Plane Failure
1 The R4 LSR control plane restarts.
2 LIB is lost when the control plane restarts.
3 The forwarding states installed by the R4 LDP control plane are immediately deleted.
4 Any in-transit packets flowing from R3 to R4 (still labeled with L4) arrive at R4.
5 The MPLS forwarding plane at R4 performs a lookup on local label L4 which fails. Because of this failure,
the packet is dropped and NSF is not met.
6 The R3 LDP peer detects the failure of the control plane channel and deletes its label bindings from R4.
7 The R3 control plane stops using outgoing labels from R4 and deletes the corresponding forwarding state
(rewrites), which in turn causes forwarding disruption.
8 The established LSPs connected to R4 are terminated at R3, resulting in broken end-to-end LSPs from R1
to R4.
9 The established LSPs connected to R4 are terminated at R3, resulting in broken LSPs end-to-end from R2
to R4.
OL-28381-02
Cisco ASR 9000 Series Aggregation Services Router MPLS Configuration Guide, Release 4.3.x
LDP Graceful Restart
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