220-1101 Question 144
Single answerPrivate addressesA technician is configuring a small office router for a new internal network. The ISP assigned the business a single public IPv4 address for internet access, and the technician wants all office PCs, printers, and phones to use private IPv4 addresses behind the router. Which of the following IP addresses is the BEST choice to assign to an internal workstation?
- A
10.25.14.8
- B
169.254.10.20
- C
172.40.5.12
- D
203.0.113.25
Show answer and explanation
Correct answer: A
Explanation
Private IPv4 addressing for internal networks is defined by RFC 1918. The three private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. In a typical small office, internal devices use one of these ranges, and the router translates those private addresses to the organization's public IPv4 address using Network Address Translation (NAT). APIPA addresses in 169.254.0.0/16 are link-local fallback addresses, not a best-practice choice for normal LAN design. When troubleshooting or configuring hosts for A+ Core 1 scenarios, candidates should be able to distinguish true private ranges from link-local, public, and documentation-only addresses.
- A. Correct.
Correct. 10.25.14.8 is within the RFC 1918 private IPv4 range 10.0.0.0 through 10.255.255.255 (10.0.0.0/8). This makes it appropriate for an internal workstation on a private LAN that will access the internet through the router using NAT.
- B. Incorrect.
Incorrect. 169.254.10.20 is an APIPA/link-local address from the 169.254.0.0/16 range. Windows and other devices typically self-assign this range when they cannot reach a DHCP server. Although it is not publicly routable, it is not the best choice for a planned internal addressing scheme because it indicates a fallback configuration rather than a properly designed private network.
- C. Incorrect.
Incorrect. 172.40.5.12 is not in the private 172.16.0.0/12 block. The private range is only 172.16.0.0 through 172.31.255.255. A common mistake is assuming any address beginning with 172 is private, but only that specific subset is reserved for private use under RFC 1918.
- D. Incorrect.
Incorrect. 203.0.113.25 is not a private IPv4 address. The 203.0.113.0/24 block is reserved for documentation and examples, not for private LAN use. It is not one of the RFC 1918 private address ranges that should be assigned to internal hosts.