hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An enterprise is using IPv6-to-IPv4 translation…
An enterprise is using IPv6-to-IPv4 translation tunneling (NAT64) but users report that they cannot reach IPv6-only servers. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source 192.0.2.1 tunnel destination 198.51.100.1 nat64 enable. Router R2 shows: R2# show nat64 translations % No translations. R2# debug nat64 all NAT64: No mapping found for packet. What is the root cause?
⚠ Common exam trap
Cisco often tests the distinction between enabling NAT64 on an interface and actually configuring the required NAT64 prefix, leading candidates to assume that 'nat64 enable' alone is sufficient.
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
✓
The NAT64 prefix is not configured under the tunnel interface.
NAT64 requires a NAT64 prefix to be explicitly configured under the tunnel interface using the 'nat64 prefix' command. Without this prefix, the router cannot construct the IPv6 representation of IPv4 destinations, so no translation mappings are created, and packets are dropped. The debug output confirms 'No mapping found for packet', which directly points to the missing prefix configuration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The NAT64 prefix is not configured under the tunnel interface.
Why this is correct
Without a NAT64 prefix, the router cannot create mappings for translation.
- ✗
The tunnel mode should be ipv6ip for NAT64 to work.
Why it's wrong here
NAT64 works with GRE or other tunnel modes; ipv6ip is not required.
- ✗
The IPv4 address of the destination server is not reachable.
Why it's wrong here
The debug shows no mapping, not unreachability.
- ✗
NAT64 is not supported on tunnel interfaces.
Why it's wrong here
NAT64 is supported on tunnel interfaces with appropriate configuration.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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