How many bits is the address space reserved for the source IP address within an IPv6 header?

A.
128

B.
32

C.
64

D.
256

Explanation:
Compared to IPv4, IPv6 increases the IP address size from 32 bits to 128 bits to support more levels of
addressing hierarchy, a much greater number of addressable nodes, and simpler autoconfiguration of
addresses.
Incorrect Answers:
B: IPv4 uses 32 bits, but IPv6 uses 128 bits.
C: IPv6 uses 128 bits, not 64 bits.
D: IPv6 uses 128 bits, not 256 bits.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, New York, 2013, p. 544