350-501 6PE Practice Question
An ISP is implementing 6PE to provide IPv6 connectivity over an MPLS network that only supports IPv4 in the core. In 6PE, how are IPv6 prefixes carried across the MPLS backbone?
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
✓
IPv6 prefixes are carried as IPv6 prefixes in MP-BGP with an IPv4 next-hop
6PE uses MP-BGP to carry IPv6 prefixes (using the IPv6 unicast address family, AFI=2 SAFI=1) with an IPv4 next-hop address (the loopback of the peer 6PE router). The BGP session is over IPv4, but the NLRI carries IPv6 prefixes. MPLS labels are used to forward traffic across the IPv4-only core. It is important to note that 6PE does not use the VPNv6 address family (AFI=1 SAFI=128) — that is used for MPLS L3VPN.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
IPv6 prefixes are transported over an IPv6 MPLS core using LDPv6
Why it's wrong here
6PE assumes the core is IPv4 MPLS.
- ✓
IPv6 prefixes are carried as IPv6 prefixes in MP-BGP with an IPv4 next-hop
Why this is correct
Correct; 6PE uses MP-BGP with AFI=2 (IPv6) and SAFI=1, with next-hop as IPv4 address.
- ✗
IPv6 prefixes are encapsulated in IPv4 tunnels with GRE
Why it's wrong here
6PE does not use GRE; it relies on MPLS and BGP.
- ✗
IPv6 prefixes are converted to IPv4 using NAT64 before MPLS forwarding
Why it's wrong here
NAT64 is not used in 6PE.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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