CompTIA A+ Core 1 (220-1201)NetworkingHard
A technician is assigned the IPv6 network 2001:db8:acad:1::/64 and needs to further divide it into 16 equal-sized subnets for different departments. What subnet prefix length should the technician use for each subnet?
- A/60
- B/68
- C/64
- D/70
Show answer & explanationAnswer & explanation
Correct answer: B. /68
To create 16 equal subnets, the technician needs 4 additional bits (2^4 = 16), so the prefix length increases from /64 to /68, giving 16 subnets of equal size.
Why the other options are wrong
- A. /60 borrows 4 bits from a /64 network in the wrong direction, producing 16 larger networks, not subnets of /64.
- C. /64 is the original prefix and does not create any additional subnets.
- D. /70 borrows 6 bits (2^6=64 subnets), producing far more than the required 16 subnets.
IPv6 Subnetting
IPv6 subnets are created by extending the prefix length; the number of subnets created equals 2 raised to the number of borrowed bits.
- 2^n subnets are created when borrowing n bits
- /64 is the standard IPv6 subnet size, borrowing bits extends it
- Formula: prefix length = original prefix + borrowed bits
Memory trick: '2 to the borrowed bits' unlocks the subnet count — 4 bits opens 16 doors.