SD-WAN TLOC Extensions for Internet Breakout

300-420 By islever Editorial Last updated

Describe Cisco SD-WAN architecture (orchestration plane, management plane, control plane, data plane, on-boarding and provisioning, security) Describe Cisco SD-WAN design considerations (control plane design, overlay design, LAN design, high availability, redundancy, scalability, security design, QoS and multicast over SD-WAN fabric)

Short answer

D TLOC extensions are used to route traffic to a WAN Edge router that is connected to the Internet transport network.

Question

How is Internet access provided to a WAN Edge router that is connected to a MPLS transport link?
  1. OMP advertises a default route from a WAN Edge router that is connected to the MPLS and Internet transport networks.
  2. Internet access must be provided at the WAN Edge router through either a 4G/5G link or local Internet circuit.
  3. An extranet must be provided in the MPLS transport network to allow private traffic to reach the public Internet.
  4. TLOC extensions are used to route traffic to a WAN Edge router that is connected to the Internet transport network. Correct Answer

Key Takeaways

The main trap is confusing general default route propagation with the specific architectural mechanism (TLOC extensions) required to make an MPLS-only router appear as an Internet exit point.

Learn how TLOC extensions enable Internet access for MPLS-only WAN Edge routers by extending TLOC advertisements to adjacent Internet-connected peers in Cisco SD-WAN.

Common mistake: Option A is the most plausible wrong answer because candidates know that default routes are advertised via OMP, but they miss that TLOC extensions are the prerequisite for the MPLS-only router to utilize the local Internet connection.

Expert Analysis

The correct answer is D. This question tests the specific Cisco SD-WAN architecture feature known as TLOC Extensions (Transport Locator Extensions). In a typical SD-WAN design, if a WAN Edge router has only an MPLS transport link, it cannot terminate Internet-bound traffic directly because it lacks a public IP interface. However, at the same physical site, another WAN Edge router might have both MPLS and Internet transports.

TLOC extensions allow these two adjacent routers to appear as a single logical entity to the rest of the SD-WAN fabric. The router with Internet access advertises its TLOC with an extension that links it to the MPLS-only router. Consequently, OMP (Overlay Management Protocol) distributes this extended TLOC information. Other WAN Edge routers in the fabric see the MPLS-only router as having Internet reachability via the extended TLOC. They route Internet-bound traffic over the MPLS tunnel to the local router, which then forwards it out the Internet interface locally.

Why not A? While advertising a default route via OMP is part of how Internet routing works, Option A implies the MPLS-connected router itself advertises the default route or that this is the primary mechanism for providing access. It fails to address the architectural bridge between the MPLS-only device and the Internet-capable device at the same site. Without TLOC extensions, the MPLS-only router would not be able to send traffic to the Internet-capable peer effectively as a unified exit point.

Why not B? The question asks how access is provided given the current connectivity, not what hardware must be added. Adding a 4G/5G link changes the scenario rather than solving the existing topology's routing challenge.

Why not C? Extranets are for private partner access, not public Internet access.

This knowledge covers the distinction between standard TLOCs and extended TLOCs, crucial for designing efficient branch architectures where Internet breakout is localized but control plane consistency is maintained across multiple devices at one site.

Exam Strategy

When analyzing SD-WAN traffic flow questions, always identify the transport types available at each site first. If a device lacks a direct Internet path but needs to send Internet traffic, look for mechanisms that extend its reachability to a peer with Internet access. Remember that TLOC extensions specifically solve the 'local breakout from an MPLS-only site' problem by making adjacent routers share TLOC attributes.

Frequently Asked Questions

What is the primary purpose of TLOC extensions in SD-WAN?

TLOC extensions allow adjacent WAN Edge routers at the same physical site to share their Transport Locator (TLOC) attributes. This enables an MPLS-only router to leverage the Internet connection of a co-located peer for traffic forwarding.

Can I use BGP to route Internet traffic from an MPLS-only router?

While BGP can be used for peering, in SD-WAN, TLOC extensions are the native mechanism for handling local Internet breakout scenarios where one router handles Internet and another handles MPLS, ensuring seamless overlay integration without complex external routing protocols.

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Community Votes

A
63%
D
25%
B
12%

63% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 11 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 11

  1. Sickcnt 👍 5 Answered D
    "What is TLOC Extension? TLOC extension is a feature that allows a WAN Edge router to communicate over the WAN transport connected to the adjacent WAN Edge router through a TLOC-extension interface" Link: https://www.networkacademy.io/ccie-enterprise/sdwan/tloc-extension
  2. Clauster 👍 4 Answered D
    This question is a very good question, but the answer is TLOC Extensions, these guys explain it in such way here is amazing and it then clicks: https://www.networkacademy.io/ccie-enterprise/sdwan/tloc-extension
  3. salmarin 👍 3 Answered A
    Traffic can route to internet via a central router that have internet via advertising a default route via OMP.
  4. certstudent2016 👍 3
    D is correct!! https://www.ciscolive.com/c/dam/r/ciscolive/us/docs/2018/pdf/BRKRST-2091.pdf
  5. rickyarchi 👍 2 Answered A
    T-LOC extension is for providing high availability when two EDGEs are connected to two different circuits. It allows to use the pair router as an underlay.
Show 6 more comments
  1. cerifyme85 👍 2 Answered B
    Not sure I agree.. the question says a WAN edge router not 2.. and also "how is internet provided"? I am taking a stab for B
  2. bubd 👍 1
    Correct: B When a WAN Edge router is connected to an MPLS transport link and you want to provide Internet access to it, the typical approach is: B. Internet access must be provided at the WAN Edge router through either a 4G/5G link or a local Internet circuit. In this scenario, the WAN Edge router is connected to the MPLS network for private traffic but needs a separate Internet connection to access the public Internet. This can be achieved through a 4G/5G cellular link or a dedicated local Internet circuit, allowing the router to route traffic to the public Internet while using the MPLS network for private traffic.
  3. NoHombre 👍 1 Answered A
    That dual-connected WAN Edge advertises a default route (0.0.0.0/0) into the SD-WAN overlay via OMP (Overlay Management Protocol). Other WAN Edges that only have MPLS learn this default via OMP. They then forward Internet-bound traffic across the MPLS transport to the dual-connected site, which exits locally to the Internet. Why not D? TLOC extensions extend transport interfaces between adjacent routers at a site. They don’t provide Internet reachability across the SD-WAN fabric on their own; you still need the OMP-advertised default route.
  4. G_Singh12 👍 1 Answered A
    TLOC extensions are used to share physical transport links locally between two adjacent routers at the exact same physical site (e.g., routing internet traffic from an MPLS-only router to a co-located internet-connected router inside the same server rack). They do not solve the broader architectural requirement of providing fabric-wide internet connectivity across a distributed network on their own.
  5. night_wolf_in 👍 1 Answered A
    TLOC used for vedge to build tunnels through secondary link on secondary vedge device.
  6. salmarin 👍 1
    exactly, one router not two , don't know how some people thing and answer.

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