How many bits are in an IPv6 address?

How many bits are in an IPv6 address?

• A. 32
• B. 64
• C. 256
• D. 128

Answer: (D)

IPv6 addresses are 128 bits long. This comes from eight groups of four hexadecimal digits, and each hex digit represents four bits, so eight groups × four digits × four bits equals 128 bits in total. The standard textual form is eight groups of four hex digits separated by colons, like 2001:0db8:85a3:0000:0000:8a2e:0370:7334, and you can shorten it by dropping leading zeros and using :: to compress a run of zeros once. This length gives a vastly larger address space than IPv4, which is 32 bits. Some parts of an IPv6 address can be 64 bits each (the network prefix and the interface identifier), but the whole address sums to 128 bits, not 256. If it were 256 bits, you’d see addresses written with 64 hex digits instead of 32.

IPv6 addresses are 128 bits long. This comes from eight groups of four hexadecimal digits, and each hex digit represents four bits, so eight groups × four digits × four bits equals 128 bits in total. The standard textual form is eight groups of four hex digits separated by colons, like 2001:0db8:85a3:0000:0000:8a2e:0370:7334, and you can shorten it by dropping leading zeros and using :: to compress a run of zeros once.

This length gives a vastly larger address space than IPv4, which is 32 bits. Some parts of an IPv6 address can be 64 bits each (the network prefix and the interface identifier), but the whole address sums to 128 bits, not 256. If it were 256 bits, you’d see addresses written with 64 hex digits instead of 32.