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300-410 Practice Question: In a 6to4 tunnel, what is the default IPv6 prefix…
In a 6to4 tunnel, what is the default IPv6 prefix assigned to the tunnel interface?
⚠ Common exam trap
Cisco often tests the distinction between the 6to4 prefix range (2002::/16) and the actual prefix assigned to the tunnel interface (2002:IPv4-address::/48), leading candidates to mistakenly select the broader /16 prefix instead of the correct /48 derived from the IPv4 address.
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
✓
2002:IPv4-address::/48
In a 6to4 tunnel, the default IPv6 prefix assigned to the tunnel interface is 2002:IPv4-address::/48, where the IPv4 address of the tunnel source is embedded in the prefix. This is defined in RFC 3056, which specifies that the 6to4 prefix is 2002::/16, and the next 32 bits are the tunnel source's IPv4 address, resulting in a /48 prefix for the 6to4 site.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
2002::/16
Why it's wrong here
2002::/16 is the prefix for 6to4, but the tunnel interface uses a /48 derived from the source IPv4 address.
- ✓
2002:IPv4-address::/48
Why this is correct
The tunnel interface gets a /48 prefix based on its source IPv4 address.
- ✗
2001::/32
Why it's wrong here
2001::/32 is used for Teredo, not 6to4.
- ✗
3ffe::/16
Why it's wrong here
3ffe::/16 was used for 6bone, not 6to4.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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