Quick Answer
The correct answer is 6PE (IPv6 Provider Edge) because it enables IPv6 traffic to traverse an existing MPLS/IPv4 backbone by requiring only the Provider Edge routers to be dual-stacked, while the core P routers remain IPv4-only and unaware of IPv6. This works by encapsulating IPv6 packets in MPLS labels at the ingress PE and stripping them at the egress PE, leveraging the existing MPLS infrastructure without upgrading the entire core. On the Cisco SPCOR 350-501 exam, this question tests your understanding of IPv6 transition mechanisms in a service provider context, often appearing as a scenario where you must choose the most scalable solution for an MPLS core. A common trap is confusing 6PE with 6VPE, which adds VPN support, or with 6to4, which requires tunnel endpoints. Remember the key distinction: 6PE keeps the core clean—only the edges speak IPv6. Memory tip: “6PE = Provider Edge only, P routers stay pure.”
This 350-501 practice question tests your understanding of architecture. 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.
A service provider is implementing IPv6 transition in its core. Which transition mechanism is recommended for carrying IPv6 over an existing MPLS/IPv4 backbone without dual-stacking all routers?
ISATAP
Why wrong: ISATAP is for site-level tunneling, not backbone.
NAT64
Why wrong: NAT64 translates IPv6 to IPv4, not a backbone transition.
6to4 tunneling
Why wrong: 6to4 requires configured tunnels and public IPv4 addresses.
6PE (IPv6 Provider Edge)
6PE uses MPLS labels; only PEs need dual-stack.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
6PE (IPv6 Provider Edge)
Option B is correct because 6PE (IPv6 Provider Edge) allows IPv6 over MPLS with only PE routers dual-stacked. Option A is wrong because 6to4 requires encapsulation endpoints. Option C is wrong because NAT64 is for translation. Option D is wrong because ISATAP is for intra-site.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
ISATAP
Why it's wrong here
ISATAP is for site-level tunneling, not backbone.
NAT64
Why it's wrong here
NAT64 translates IPv6 to IPv4, not a backbone transition.
6to4 tunneling
Why it's wrong here
6to4 requires configured tunnels and public IPv4 addresses.
6PE (IPv6 Provider Edge)
Why this is correct
6PE uses MPLS labels; only PEs need dual-stack.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Architecture — study guide chapter
Learn the concepts, then practise the questions
Architecture practice questions
Targeted practice on this topic area only
All 350-501 questions
500 questions across all exam domains
Cisco SPCOR / CCNP Service Provider Core 350-501 study guide
Full concept coverage aligned to exam objectives
350-501 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise 350-501 questions linked to Architecture.
Practise 350-501 questions linked to Networking.
Practise 350-501 questions linked to MPLS and Segment Routing.
Practise 350-501 questions linked to Automation and Quality of Service.
Practise 350-501 questions linked to Services.
Practise 350-501 questions linked to Automation and Assurance.
Practise 350-501 questions linked to 350-501 fundamentals.
Practise 350-501 questions linked to 350-501 scenario.
Practise 350-501 questions linked to 350-501 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Architecture — This question tests Architecture — Static NAT maps one inside address to one outside address..
The correct answer is: 6PE (IPv6 Provider Edge) — Option B is correct because 6PE (IPv6 Provider Edge) allows IPv6 over MPLS with only PE routers dual-stacked. Option A is wrong because 6to4 requires encapsulation endpoints. Option C is wrong because NAT64 is for translation. Option D is wrong because ISATAP is for intra-site.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 24, 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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.