MPLS and RSVP
7210 SAS M, T, X, R6, Mxp MPLS Configuration Guide Page 27
FRR Node-Protection (Facility)
The MPLS Fast Re-Route (FRR) functionality enables PLRs to be aware of the missing node
protection and lets them regularly probe for a node-bypass. The following describes an LSP
scenario:
Figure 4: FRR Node-Protection Example
Where:
• LSP 1: between PE_1 to PE_2, with CSPF, FRR facility node-protect enabled.
• P_1 protects P_2 with bypass-nodes P_1 -P_3 - P_4 - PE_4 -PE_2.
• If P_4 fails, P_1 tries to establish the bypass-node three times.
• When the bypass-node creation fails, P_1 will protect link P_1-P_2.
• P_1 protects the link to P_2 through P_1 - P_5 - P_2.
• P_4 returns online.
Since LSP 1 had requested node protection, but due to lack of any available path, it could only
obtain link protection. Therefore, every 60 seconds the PLR for LSP 1 will search for a new path
that might be able to provide node protection. Once P_4 is back online and such a path is
available, A new bypass tunnel will be signalled and LSP 1 will get associated with this new
bypass tunnel.
Uniform FRR Failover Time
The failover time during FRR consists of a detection time and a switchover time. The detection
time corresponds to the time it takes for the RSVP control plane protocol to detect that a network
IP interface is down or that a neighbor/next-hop over a network IP interface is down. The control
plane can be informed of an interface down event when event is due to a failure in a lower layer
such in the physical layer. The control plane can also detect the failure of a neighbor/next-hop on
its own by running a protocol such as Hello, Keep-Alive, or BFD.
P_5
PE_1
PE_3
P_1
P_3
P_2
P_4
PE_2
PE_4
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