CCNA DC FAQ: Fundamentals of IP Version 6

CCNA Data Center FAQ: Fundamentals of IP Version 6


Figure: Example of Static IPv6 Addresses

Q1. Of the following list of motivations for the Internet community to create IPv6 to replace IPv4, which was the most important reason?
a. To remove the requirement to use NAT when connecting to the Internet
b. To simplify the IP header to simplify router-forwarding CPU time
c. To improve support to allow mobile devices to move into a network
d. To provide more addresses to relieve the address-exhaustion problem

Answer: D. The most compelling reason was the address-exhaustion problem. The rest of the motivations are true motivations and benefits of IPv6 as well.

Q2. Which of the following is the shortest valid abbreviation for FE80:0000:0000:0100:0000:0000:0000:0123?
a. FE80::100::123
b. FE8::1::123
c. FE80::100:0:0:0:123:4567
d. FE80:0:0:100::123

Answer: D. If following the steps in the book, the first step removes up to three leading 0s in each quartet, leaving FE80:0:0:100:0:0:0:123. This leaves two strings of consecutive all-0 quartets; by changing the longest string of all 0s to ::, the address is FE80:0:0:100::123.

Q3. Which of the following is the shortest valid abbreviation for 2000:0300:0040:0005:6000:0700:0080:0009?
a. 2:3:4:5:6:7:8:9
b. 2000:300:40:5:6000:700:80:9
c. 2000:300:4:5:6000:700:8:9
d. 2000:3:4:5:6:7:8:9

Answer: B. This question has many quartets that make it easy to make a common mistake: removing trailing 0s in a quartet of hex digits. To abbreviate IPv6 addresses, only leading 0s in a quartet should be removed. Many of the quartets have trailing 0s (0s on the right side of the quartet), so make sure to not remove those 0s.

Q4. Which of the following is the prefix for address 2000:0000:0000:0005:6000:0700:0080:0009, assuming a mask of /64?
a. 2000::5::/64
b. 2000::5:0:0:0:0/64
c. 2000:0:0:5::/64
d. 2000:0:0:5:0:0:0:0/64

Answer: C. The /64 prefix length means that the last 64 bits, or last 16 digits, of the address should be changed to all 0s. That process leaves the unabbreviated prefix as 2000:0000:0000:0005:0000:0000:0000:0000. The last four quartets are all 0s, making that string of all 0s the longest and best string of 0s to replace with ::. After you remove the leading 0s in other quartets, the answer is 2000:0:0:5::/64.

Q5. Which of the following IPv6 addresses appears to be a global unicast address, based on its first few hex digits?
a. 3123:1:3:5::1
b. FE80::1234:56FF:FE78:9ABC
c. FDAD::1
d. FF00::5

Answer: A. Global unicast addresses can begin with many different initial values, but most commonly, they begin with either a hex 2 or 3.

Q6. When subnetting an IPv6 address block, an engineer shows a drawing that breaks the address structure into three pieces. Comparing this concept to a three-part IPv4 address structure, which part of the IPv6 address structure is most like the IPv4 network part of the address?
a. Subnet
b. Interface ID
c. Network
d. Global routing prefix
e. Subnet router anycast

Answer: D. The global routing prefix is the address block, represented as a prefix value and prefix length, given to an organization by some numbering authority. All IPv6 addresses inside the company have the same value in these initial bits of their IPv6 addresses. Similarly, when a company uses a public IPv4 address block, all the addresses have the same value in the network part.

Q7. When subnetting an IPv6 address block, an engineer shows a drawing that breaks the address structure into three pieces. Assuming that all subnets use the same prefix length, which of the following answers lists the name of the field on the far right side of the address?
a. Subnet
b. Interface ID
c. Network
d. Global routing prefix
e. Subnet router anycast

Answer: B. Subnetting a global unicast address block, using a single prefix length for all subnets, breaks the addresses into three parts. The parts are the global routing prefix, subnet, and interface ID.

Q8. Host PC1 dynamically learns its IPv6 settings using stateless address autoconfiguration (SLAAC). Think about the host’s unicast address as two parts: the prefix and the interface ID. Which of the answers list a way that SLAAC learns or builds the value of the interface ID portion of the host’s address? (Choose two answers.)
a. Learned from a DHCPv6 server
b. Built by the host using EUI-64 rules
c. Learned from a router using NDP RS/RA messages
d. Built by the host using a random value

Answer: B and D. With SLAAC, the host learns the prefix from a router using NDP RS/RA messages, and then the host builds the rest of the address (the interface ID). The host can use EUI-64 rules, or use a defined process to randomly generate the interface ID value. The host does not learn the interface ID from any other device, which helps make the process stateless, because no other device needs to assign the host its full address.

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James Palmer

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