300-410 Layer 3 Technologies Practice Question
A network administrator is implementing MPLS Layer 3 VPNs. The administrator wants to ensure that customer routes are not leaked between different VRFs on the same PE router. Which mechanism should be used to isolate the VRFs?
⚠ Common exam trap
Many exam-takers confuse route distinguishers with route targets; RDs make prefixes unique, but route targets control import/export.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Route targets
Route targets are extended BGP communities that define which VRFs can import and export routes. By configuring distinct route targets for each VRF, you control route distribution and prevent leaking. Route distinguishers only make prefixes unique, MPLS labels are for forwarding, and standard BGP communities are not specific to VRF isolation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
BGP communities
Why it's wrong here
Standard BGP communities can be used for tagging routes, but they are not the primary mechanism for VRF route import/export. Route targets are a specific type of extended community used for this purpose. While BGP communities can influence routing policies, they do not inherently isolate VRFs. Thus, this option is not correct.
- ✗
Route distinguishers
Why it's wrong here
Route distinguishers (RDs) are used to make VPNv4 prefixes unique across the MPLS VPN domain. They are prepended to the customer prefix to create a unique VPNv4 address. However, RDs do not control import/export of routes between VRFs; that is the role of route targets. Using only RDs without route targets would not prevent route leaking if route targets are misconfigured. Thus, RDs alone are not sufficient.
- ✓
Route targets
Why this is correct
Route targets are extended BGP communities used to control the import and export of routes between VRFs. By assigning unique route targets to each VRF, you ensure that routes from one VRF are not imported into another. This provides the necessary isolation. Without proper route target configuration, routes could leak. Therefore, route targets are the correct mechanism.
- ✗
MPLS labels
Why it's wrong here
MPLS labels are used for forwarding packets within the MPLS domain, but they do not provide VRF isolation. Labels are assigned based on the next-hop and are swapped at each hop. They do not control route distribution or import/export policies. Therefore, MPLS labels are not the mechanism for isolating VRFs.
Go deeper
Related to this question
Learn chapter
BGP Route Selection and Policy
Key term
BGP Communities
BGP communities are tags attached to routes that allow routers to apply common policies across networks without manual per-route configuration.
Key term
MPLS Layer 3 VPN
A technology that uses Multiprotocol Label Switching to create secure, scalable virtual private networks that connect multiple sites at the network layer, where the service provider manages routing between customer sites.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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