A small clinic has one WAN Edge with only a single MPLS circuit, while a neighboring admin router on the same LAN has both MPLS and internet transports. The clinic must use the neighbor's internet without adding a circuit. Which TLOC extension design lets a router borrow another router's transport and how is it configured?

The correct design is right because TLOC extension lets a constrained router borrow a neighbor transport over a shared LAN without adding a circuit, built as an extension interface in VPN 0 on both peers with the borrower configured for the missing color, here internet, so its control connections and IPsec tunnels can egress through the neighbor internet TLOC while its own MPLS TLOC remains for primary paths. The distractor that extends MPLS for resiliency describes a valid and common use for redundancy but fails by transport concept because the clinic already has MPLS locally and specifically needs internet diversity, so repeating the same color adds no new overlay path. The distractor that places the extension in a service VPN sounds plausible because service VPNs interconnect LANs daily, but it fails by architecture because TLOCs, tunnel interfaces and IPsec encapsulation exist only in VPN 0, so an extension outside VPN 0 cannot establish control connections or carry overlay data. The distractor that has the admin router borrow clinic MPLS reverses a legitimate sharing pattern but fails by directionality and scenario fact, since the requirement is for the single-circuit clinic to gain internet, not for the already dual-transport neighbor to gain another MPLS path. For exams, do not confuse TLOC extension with DIA, NAT or route sharing, remember color binding defines which transport is borrowed and VPN 0 placement is mandatory. Practically, verify on the borrower with show control connections and tunnel state to confirm the internet TLOC is up via the extension next hop, then test resilience by shutting MPLS and confirming overlay traffic sustains over borrowed internet.