350-501 · Question #159
Which three statements about the Cisco MPLS TE Fast Reroute (FRR) process are true? (Choose three.)
The correct answer is A. TE tunnels that are configured with the FRR option cannot be used as backup tunnels. C. The backup tunnel that is used to protect a physical interface must have a valid IP address D. Interfaces must use MPLS global label allocation. MPLS TE FRR uses RSVP to reserve bandwidth for tunnels, and these tunnels are unidirectional, meaning separate tunnels are needed for bidirectional traffic flow; tunnels configured with FRR cannot serve as backup tunnels themselves.
Question
Which three statements about the Cisco MPLS TE Fast Reroute (FRR) process are true? (Choose three.)
Options
- ATE tunnels that are configured with the FRR option cannot be used as backup tunnels.
- BTE tunnels that are configured with the FRR option can be used as backup tunnels.
- CThe backup tunnel that is used to protect a physical interface must have a valid IP address
- DInterfaces must use MPLS global label allocation.
- EThe source IP address of use backup tunnel and the merge point (MP) should not be reachable.
How the community answered
(33 responses)- A82% (27)
- B6% (2)
- E12% (4)
Why each option
MPLS TE FRR uses RSVP to reserve bandwidth for tunnels, and these tunnels are unidirectional, meaning separate tunnels are needed for bidirectional traffic flow; tunnels configured with FRR cannot serve as backup tunnels themselves.
TE tunnels configured with the FRR option are primary tunnels that are protected by backup tunnels; they cannot simultaneously serve as backup tunnels for other primary tunnels.
TE tunnels configured with FRR are the primary tunnels that are *protected* by backup tunnels, not used *as* backup tunnels themselves.
For a backup tunnel to effectively protect an interface, the ingress and egress points of the protected LSP (and thus implicitly the reachability targets for the backup tunnel signaling) must be IP reachable, and often, the logical tunnel interface may be configured with an IP address as part of the overall TE setup or for management.
MPLS Traffic Engineering (TE) typically operates within a global, platform-wide label space, meaning interfaces must be configured to use this global label allocation for RSVP-TE to signal and manage labels effectively.
The source IP address of the backup tunnel (Point of Local Repair - PLR) and the merge point (MP) must be reachable for the backup path to be signaled and utilized effectively in case of a failure.
Concept tested: MPLS TE Fast Reroute (FRR) characteristics
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_te_frr/configuration/15-mt/mp-te-frr-15-mt-book/mp-te-frr.html
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