350-501 Architecture Practice Question
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?
⚠ Common exam trap
Cisco often tests the distinction between mechanisms that require dual-stack on all routers (like 6to4 or ISATAP) versus those that only require dual-stack on edge routers (like 6PE), so the trap here is assuming that any tunneling mechanism works without considering the MPLS core requirement.
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
✓
6PE (IPv6 Provider Edge)
6PE (IPv6 Provider Edge) is the correct answer because it allows IPv6 traffic to be carried over an existing MPLS/IPv4 backbone without requiring dual-stack on all core routers. In 6PE, only the Provider Edge (PE) routers need to be dual-stack; they encapsulate IPv6 packets in MPLS labels and transport them across the IPv4 MPLS core, which remains IPv4-only. This meets the requirement of not dual-stacking all routers while leveraging the existing MPLS infrastructure.
Answer analysis
Option-by-option breakdown
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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