300-410 Infrastructure Services Practice Question
A network engineer is configuring a Cisco IOS router to support MPLS L3VPN. The router will act as a PE router and needs to assign a unique identifier to each customer VRF to allow overlapping address spaces. Which MPLS L3VPN component provides this function?
⚠ Common exam trap
Candidates often confuse the Route Distinguisher with the Route Target, as both are BGP attributes used in MPLS L3VPN but serve different purposes.
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 Distinguisher
The Route Distinguisher (RD) is the MPLS L3VPN component that provides a unique identifier for each customer VRF, allowing overlapping IPv4 address spaces. By prepending the RD to customer prefixes, MP-BGP creates VPNv4 routes that are globally unique. This enables the service provider to carry multiple customers' routes without conflict. The RD is configured under the VRF definition and is essential for MPLS L3VPN operation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Route Target
Why it's wrong here
A Route Target is a BGP extended community used to control the import and export of routes between VRFs. It does not provide a unique identifier for a VRF to allow overlapping addresses. Instead, it defines VPN membership and influences route distribution. The component that makes customer prefixes unique across the MPLS domain is the Route Distinguisher, not the Route Target.
- ✗
VPN Label
Why it's wrong here
The VPN Label is a label used within the MPLS forwarding plane to identify the VRF or the egress interface for a packet. It is assigned by the egress PE router and is used for forwarding, not for making prefixes unique. While essential for MPLS L3VPN operation, it does not provide the address disambiguation function that the Route Distinguisher does.
- ✗
BGP Extended Community
Why it's wrong here
BGP Extended Communities are attributes used for various purposes, including Route Targets for VPN membership. They do not serve as a unique identifier for VRFs to handle overlapping addresses. The Route Distinguisher is the specific component that ensures uniqueness. Extended communities like Route Targets are used for route import/export policies, not for address disambiguation.
- ✓
Route Distinguisher
Why this is correct
The Route Distinguisher (RD) is an 8-byte value prepended to an IPv4 prefix to make it unique within the MPLS L3VPN domain. It allows different customers to use the same address space without conflict. Each VRF is assigned an RD, which is used in MP-BGP VPNv4 updates. Without an RD, overlapping customer prefixes would be ambiguous in the provider's BGP table.
Go deeper
Related to this question
Learn chapter
EIGRP Route Summarization and Filtering
Key term
MP-BGP for VPN
MP-BGP for VPN is an extension of the Border Gateway Protocol that carries multiple types of network layer information to enable scalable, isolated virtual private networks over a shared provider infrastructure.
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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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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