350-501 · Question #230
A network engineer has configured TE tunnels in the MPLS provider core. Which two steps ensure traffic traverse? (Choose two.)
The correct answer is C. Forwarding adjacency features allows a tunnel to be installed in the IGP table as a link. D. The IGP metric of a tunnel is configured to prefer a certain path. To ensure traffic traverses MPLS TE tunnels, the tunnels must be integrated into the IGP's topology as logical links, and their IGP metrics must be configured to influence path selection.
Question
A network engineer has configured TE tunnels in the MPLS provider core. Which two steps ensure traffic traverse? (Choose two.)
Options
- AStatic routes is the only option for directing traffic into a tunnel.
- BECMP between tunnels allows RSVP to function correctly.
- CForwarding adjacency features allows a tunnel to be installed in the IGP table as a link.
- DThe IGP metric of a tunnel is configured to prefer a certain path
- EA tunnel weight is configured in SPF database the same way as a native link.
How the community answered
(50 responses)- A6% (3)
- B2% (1)
- C90% (45)
- E2% (1)
Why each option
To ensure traffic traverses MPLS TE tunnels, the tunnels must be integrated into the IGP's topology as logical links, and their IGP metrics must be configured to influence path selection.
Static routes are one method but not the exclusive option for directing traffic into a TE tunnel; IGP integration via forwarding adjacency or policy-based routing are other common mechanisms.
ECMP between tunnels facilitates load balancing, but it is not directly related to ensuring RSVP (Resource Reservation Protocol) functions correctly, which is the signaling protocol for establishing the tunnels themselves.
The forwarding adjacency feature allows an MPLS Traffic Engineering (TE) tunnel to be advertised into the IGP (OSPF or IS-IS) as a virtual link. This enables the IGP to use the tunnel as part of its shortest path calculations, directing traffic into it.
Configuring a specific IGP metric for a TE tunnel influences the IGP's shortest path first (SPF) calculations. By assigning a lower metric to a tunnel, the IGP will prefer that path, ensuring traffic is steered through the desired tunnel.
The concept of 'tunnel weight' is primarily a BGP attribute and is not a mechanism configured in the SPF database to integrate a tunnel as a native link for IGP metric calculations.
Concept tested: MPLS Traffic Engineering (TE) tunnel integration with IGP
Source: https://www.cisco.com/c/en/us/td/docs/ios/mpls/configuration/guide/12_2sx/t_te.html
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