Quick Answer
The answer is the VPNv4 unicast address family. This is the mandatory BGP address family used between PE routers in an MPLS L3VPN because VPNv4 routes combine the IPv4 prefix with an 8-byte Route Distinguisher (RD), ensuring global uniqueness even when overlapping customer address spaces exist. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of how MP-BGP extends standard IPv4 routing to support MPLS VPNs, often appearing in questions about the mandatory address-family ipv4 vpn configuration under the BGP process. A common trap is confusing the VPNv4 address family with the IPv4 unicast family, but remember that only VPNv4 carries the RD needed for VRFs. For a quick memory tip: think “VPNv4 = IPv4 + RD” to recall that the VPNv4 unicast family is the only way to exchange these extended routes between PEs.
This 350-501 practice question tests your understanding of mpls and segment routing. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which BGP address family must be used to exchange VPNv4 routes between PE routers in an MPLS L3VPN?
RT constraint
Why wrong: RT constraint is used to filter route advertisements, not to exchange VPN routes.
IPv4 unicast
Why wrong: IPv4 unicast does not carry VPN attributes like RD and RT.
L2VPN VPLS
Why wrong: L2VPN address families are for Layer 2 VPN services, not Layer 3 VPN.
VPNv4 unicast
VPNv4 unicast is the correct address family for exchanging VPN-IPv4 routes.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
VPNv4 unicast
In an MPLS L3VPN, VPNv4 routes carry both the IPv4 prefix and the Route Distinguisher (RD) to ensure uniqueness across overlapping customer address spaces. The VPNv4 unicast address family (address-family ipv4 vpn) is the mandatory BGP address family used between PE routers to exchange these VPNv4 routes, enabling MPLS-based VPN reachability.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
RT constraint
Why it's wrong here
RT constraint is used to filter route advertisements, not to exchange VPN routes.
IPv4 unicast
Why it's wrong here
IPv4 unicast does not carry VPN attributes like RD and RT.
L2VPN VPLS
Why it's wrong here
L2VPN address families are for Layer 2 VPN services, not Layer 3 VPN.
VPNv4 unicast
Why this is correct
VPNv4 unicast is the correct address family for exchanging VPN-IPv4 routes.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Cisco often tests the distinction between the address family used for route exchange (VPNv4 unicast) versus the filtering mechanism (RT constraint), leading candidates to confuse the RT constraint address family as the primary exchange method.
Detailed technical explanation
VPNv4 routes are encoded with an 8-byte Route Distinguisher prepended to the IPv4 prefix, forming a 12-byte NLRI that BGP distributes within the VPNv4 address family. PE routers use MP-BGP (RFC 4760) with the AFI/SAFI 1/128 for VPNv4, and MPLS labels are carried via BGP path attributes to enable label-switched forwarding across the provider backbone.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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MPLS and Segment Routing — study guide chapter
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FAQ
MPLS and Segment Routing — This question tests MPLS and Segment Routing — Read the scenario before looking for a memorised answer..
The correct answer is: VPNv4 unicast — In an MPLS L3VPN, VPNv4 routes carry both the IPv4 prefix and the Route Distinguisher (RD) to ensure uniqueness across overlapping customer address spaces. The VPNv4 unicast address family (address-family ipv4 vpn) is the mandatory BGP address family used between PE routers to exchange these VPNv4 routes, enabling MPLS-based VPN reachability.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
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