Networking Fundamentals Practice Question 7: Private Address Ranges
Networking Fundamentals · Test 1 · question 7 of 10
An office network uses private IPv4 addresses internally, and the edge router uses NAT to translate them to its single public address. When planning a new internal subnet, which address falls inside one of the private ranges reserved for this kind of use?
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Answer:
RFC 1918 reserves three IPv4 blocks for private networks. Addresses in these blocks are never routed on the public Internet, so hosts that use them reach the Internet through NAT.
- 10.0.0.0 – 10.255.255.255 (10/8) - 172.16.0.0 – 172.31.255.255 (172.16/12) - 192.168.0.0 – 192.168.255.255 (192.168/16)
172.20.14.5 falls within 172.16.0.0 – 172.31.255.255, so A is correct.
- B. 172.32.14.5 is a common trap. The 172.16/12 block ends at 172.31.255.255, so 172.32.x.x is public address space. - C. 192.169.14.5 is outside 192.168/16. Only 192.168.x.x is private, so this is public. - D. 11.20.14.5 is outside 10/8. Only 10.x.x.x is private, so this is public.
Using public addresses internally can break access to whoever really owns those addresses on the Internet.
Reference: RFC 1918 - Address Allocation for Private Internets, section 3