Question 124 of 530 from exam 400-251: CCIE Security written exam

# Question 124 of 530 from exam 400-251: CCIE Security written exam

### Question

Given the IPv4 address 10.10.100.16, which two addresses are valid IPv4-compatible IPv6 addresses? (Choose two.)

### Explanations

Click on the arrows to vote for the correct answer

A. B. C. D.

BC.

To convert an IPv4 address to an IPv4-compatible IPv6 address, we need to place the IPv4 address in the low-order 32 bits of the IPv6 address. The high-order 96 bits are set to zero, and the 80th bit is set to one. This format is known as IPv4-compatible IPv6 address format.

So, the IPv4 address 10.10.100.16 can be represented as follows in binary:

00001010 00001010 01100100 00010000

To convert this to an IPv4-compatible IPv6 address, we insert the binary value into the low-order 32 bits of an IPv6 address, with the high-order 96 bits set to zero, and the 80th bit set to one:

0000:0000:0000:0000:0000:ffff:0a0a:6410

Now, let's look at each of the answer choices to see which ones are valid IPv4-compatible IPv6 addresses:

A. :::A:A:64:10

This is not a valid IPv4-compatible IPv6 address. The first three colons represent a sequence of zero bits, but there should be only one sequence of zero bits in an IPv6 address. Also, the "A" is not a valid hexadecimal digit.

B. ::10:10:100:16

This is a valid IPv4-compatible IPv6 address. The high-order 96 bits are represented by two colons, and the low-order 32 bits are the IPv4 address 10.10.100.16.

C. 0:0:0:0:0:10:10:100:16

This is not a valid IPv4-compatible IPv6 address. There are too many fields in this address. An IPv6 address should have only 8 fields.

D. 0:0:10:10:100:16:0:0:0

This is not a valid IPv4-compatible IPv6 address. There are too many fields in this address. An IPv6 address should have only 8 fields.

Therefore, the valid IPv4-compatible IPv6 addresses are B. ::10:10:100:16. and one other valid answer that wasn't provided in the answer choices is:

E. 0:0:0:0:0:ffff:0a0a:6410