Cisco Certified Network Associate (CCNA) Practice Exam

Which option is a valid IPv6 address?

1. 2001:0000:130F::099a::12a

2. 2002:7654:A1AD:61:81AF:CCC1

3. FEC0:ABCD:WXYZ:0067::2A4

4. 2004:1:25A4:886F::1

The correct answer is: 2004:1:25A4:886F::1

A valid IPv6 address must conform to specific formats and rules established for IPv6 addressing. The correct example meets these criteria by adhering to the following guidelines: 1. **Structure**: An IPv6 address is typically represented by eight groups of four hexadecimal digits, separated by colons. However, to accommodate for the zero compression feature, contiguous fields of zeros can be replaced with a double colon, but this can only appear once in an address. 2. **Hexadecimal digits**: Each group must only contain valid hexadecimal characters, which include the digits 0-9 and letters A-F (in either uppercase or lowercase). In the case of the address that has been identified as valid, "2004:1:25A4:886F::1," it follows all these rules. It uses the appropriate format, containing valid hexadecimal characters, and employs zero compression correctly with the double colon representing the missing groups. The other choices deviate from these rules in various ways. For example, one of the options contains a group with invalid characters (WXYZ), while another has an incorrect number of colons, indicating the use of the double colon more than once, which is not permissible. Each of these errors invalidates the addresses presented in those