Which of the following is a valid IPv6 address

Which of the following is a valid IPv6 address?

1 4021::240E::0AC0:3428
2 4021:240E::0AC0::3428
3 4021:240E::0AC0:3428:121C
4 4021::0000::240E::0000::0000:0AC0::3428::121C
5 All of the above

The Correct Answer and Explanation is :

The correct answer is 3) 4021:240E::0AC0:3428:121C.

Explanation:

IPv6 addresses are 128-bit identifiers that are usually written in hexadecimal format, separated by colons (:). To make the addresses more readable, rules have been established for abbreviating them.

Key rules for valid IPv6 addresses:

1. Colons for separation: IPv6 addresses consist of eight 16-bit groups, each represented as four hexadecimal digits. These groups are separated by colons (:).
2. Leading zeroes: Leading zeroes in any 16-bit group can be omitted. For instance, 0001 can be written as 1.
3. Double colons (::): The :: notation can be used to replace one or more consecutive groups of zeroes. However, it can only appear once in an address to avoid ambiguity.

Analysis of the options:

1. 4021::240E::0AC0:3428
   This address contains two :: groups, which is not allowed. The use of multiple :: would create ambiguity about the number of zeroes between them, so it is invalid.
2. 4021:240E::0AC0::3428
   Similar to the first option, this address has two :: groups, which makes it invalid for the same reason as above.
3. 4021:240E::0AC0:3428:121C
   This is a valid IPv6 address. It uses a single :: to represent a group of zeroes and contains the correct number of 16-bit groups (five total). The structure adheres to the rules, so it is a valid IPv6 address.
4. 4021::0000::240E::0000::0000:0AC0::3428::121C
   This address contains multiple :: groups, which is invalid for the same reason as options 1 and 2. Only one instance of :: is permitted in a valid IPv6 address.

Conclusion:

The only valid IPv6 address from the options provided is 4021:240E::0AC0:3428:121C, as it adheres to the proper syntax for abbreviated IPv6 notation and uses :: only once.