N10-009 RFC 1918 Practice Question
Which of the following IP addresses is a private IP address as defined by RFC 1918?
⚠ Common exam trap
The trap here is that candidates often remember 172.x.x.x as private but forget the specific range (172.16.0.0/12), leading them to select 172.32.1.1 or 172.15.1.1, both of which are public addresses.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
192.168.1.1
(192.168.1.1) is correct because RFC 1918 reserves the 192.168.0.0/16 block (192.168.0.0 – 192.168.255.255) for private use within local networks. This address is not routable on the public internet, making it suitable for internal LAN addressing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
169.254.1.1
Why it's wrong here
169.254.1.1 falls in the link-local range (169.254.0.0/16), which is self-assigned when DHCP fails, not an RFC 1918 private range. It is tempting because it is non-routable on the public internet like private addresses, but RFC 1918 defines only 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16.
When this WOULD be correct
This would be correct if the question asked for an APIPA address used for automatic private IP addressing when DHCP fails.
- ✗
172.32.1.1
Why it's wrong here
RFC 1918 reserves 172.16.0.0 through 172.31.255.255, so 172.32.1.1 lies beyond the upper boundary and is publicly routable. It is tempting because it shares the 172 prefix and a similar dotted form. A valid private address would have a second octet between 16 and 31 inclusive.
When this WOULD be correct
This IP would be correct if the question asked for a public IP address or an IP that is not in any private range. For example, 'Which of the following is a public IP address?'
- ✓
192.168.1.1
Why this is correct
192.168.1.1 falls within the 192.168.0.0/16 block that RFC 1918 reserves for private internets, satisfying the stem's requirement. Unlike public addresses, it is non-routable on the internet, so it only works within internal networks behind NAT.
- ✗
172.15.1.1
Why it's wrong here
RFC 1918 reserves 172.16.0.0 through 172.31.255.255, so 172.15.1.1 falls outside that block and is publicly routable. It is tempting because it sits adjacent to the private range and shares the 172 prefix. The correct private address would fall within the 172.16–172.31 second-octet span.
When this WOULD be correct
This option would be correct if the question asked for a public IP address or an IP address that is not in the RFC 1918 private ranges, as 172.15.1.1 is a public IP.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓192.168.1.1Correct answer▾
Why this is correct
192.168.1.1 falls within the 192.168.0.0/16 block that RFC 1918 reserves for private internets, satisfying the stem's requirement. Unlike public addresses, it is non-routable on the internet, so it only works within internal networks behind NAT.
✗169.254.1.1Wrong answer — click to see why▾
Why this is wrong here
169.254.1.1 is an APIPA address, not a private IP per RFC 1918. RFC 1918 defines private ranges as 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
★ When this WOULD be the correct answer
This would be correct if the question asked for an APIPA address used for automatic private IP addressing when DHCP fails.
Why candidates choose this
Candidates may confuse APIPA (169.254.0.0/16) with private IP ranges because both are non-routable on the public internet.
✗172.32.1.1Wrong answer — click to see why▾
Why this is wrong here
172.32.1.1 falls within the 172.16.0.0/12 range (172.16.0.0 to 172.31.255.255) only if the second octet is between 16 and 31. Since 32 is outside that range, it is not a private IP per RFC 1918.
★ When this WOULD be the correct answer
This IP would be correct if the question asked for a public IP address or an IP that is not in any private range. For example, 'Which of the following is a public IP address?'
Why candidates choose this
Candidates may mistakenly think that any IP starting with 172 is private, not realizing that only the 172.16.0.0/12 block is reserved.
✗172.15.1.1Wrong answer — click to see why▾
Why this is wrong here
172.15.1.1 falls within the 172.16.0.0/12 range (172.16.0.0 to 172.31.255.255) defined by RFC 1918 for private IP addresses, but 172.15.1.1 is actually in the 172.8.0.0/13 range, which is not private; it is a public IP address.
★ When this WOULD be the correct answer
This option would be correct if the question asked for a public IP address or an IP address that is not in the RFC 1918 private ranges, as 172.15.1.1 is a public IP.
Why candidates choose this
Candidates may mistakenly think that all 172.x.x.x addresses are private, not realizing that only the 172.16.0.0/12 block is reserved, and 172.15.1.1 is just outside that range.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
Learn chapter
IPv6 Addressing and Address Types
Key term
LAN
Local Area Network — a network confined to a single physical location such as an office, building, or campus.
Key term
Private IP address
A private IP address is a non-internet-routable address used within a local network to identify devices and allow them to communicate with each other without direct exposure to the public internet.
About these practice questions
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Same concept, more angles
1 more way this is tested on N10-009
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer is reviewing RFC 1918 address ranges to plan a private IP addressing scheme. Which of the following IP addresses falls within the private address space for Class A?
medium- A.172.16.0.1
- B.192.168.1.1
- ✓ C.10.10.10.1
- D.172.32.0.1
Why C: RFC 1918 defines the Class A private address range as 10.0.0.0/8, which includes all addresses from 10.0.0.0 to 10.255.255.255. 10.10.10.1 falls within this range, making it a valid private IP address for internal network use.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.