Question

If your ISP assigns you prefix 2003:1234:abcd:6600:: /56, how many bits do you have to create subnets ?

A. 4 bits

B. 8 bits

C. 12 bits

D. 16 bits

Answer 1

Answer: (B) 8 bits

Explanation:

IPv6:

• IPv6 addresses are of length 128 bits.
• IPv6 address is divided into

Network ID (64 bits)

Interface ID (64 Bits)

Network ID portion includes Global route prefix and subnet id bits.

Available bits to create subnets = Network ID bits - given prefix length

Given Address: 2003:1234:abcd:6600:: /56

Given network prefix length = 56

Available bits to create subnets = 64 - 56 = 8.

2003

${\color{Green} 1234}$

${\color{Green} abcd}$

${\color{Green} 66}{\color{Red} 00}$

${\color{Blue} 0000}$

${\color{Blue} 0000}$

${\color{Blue} 0000}$

${\color{Blue} 0000}$

Bits in green color indicates network id bits.

Bits in red color indicates bits available for subnets.

(since hex value equal to 4 binary bits, number of bits available for subnets = 2 x 4 = 8)

Bits in blue color indicates host id bits. (16 x 4 = 64 bits)

Therefore, 8 bits are available to create subnets.