The correct answer identifies 127.0.0.1 as the loopback address and 169.254.0.0/16 as the link-local range. The loopback address, 127.0.0.1, is a reserved IPv4 address used by a host to send traffic to itself for testing network stack functionality, while the 169.254.0.0/16 block is designated for Automatic Private IP Addressing (APIPA) when a device fails to obtain a DHCP lease. On the JNCIA-Junos exam, these IPv4 addressing concepts test your ability to distinguish between loopback, link-local, and private address ranges—a common trap is confusing 169.254.0.0/16 (link-local) with private ranges like 192.168.0.0/16 or 10.0.0.0/8. Remember that private addresses are routable within a local network, but link-local addresses are never routed. A useful memory tip: think of 127.0.0.1 as “home” for self-testing, and 169.254.x.x as “last resort” when DHCP fails.
JNCIA-JUNOS Networking Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of networking fundamentals. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO statements about IPv4 addressing are correct?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The network 169.254.0.0/16 is used for link-local addressing.
Options A and B are correct. 127.0.0.1 is the loopback address, and 169.254.0.0/16 is used for link-local addressing (APIPA). Option C is false because 192.168.0.0/16 is a private address. Option D is false because 10.0.0.0/8 is private. Option E is false because a /24 subnet mask provides 254 usable host addresses, not 256.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
A /24 subnet mask provides 256 usable host addresses.
Why it's wrong here
Incorrect. A /24 subnet provides 256 total addresses, but only 254 are usable (network and broadcast addresses are reserved).
✓
The network 169.254.0.0/16 is used for link-local addressing.
Why this is correct
Correct. This range is automatically assigned when no DHCP server is available.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related JNCIA-JUNOS subnetting questions on CIDR, address ranges, and subnet selection.
Networking Fundamentals — This question tests Networking Fundamentals — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The network 169.254.0.0/16 is used for link-local addressing. — Options A and B are correct. 127.0.0.1 is the loopback address, and 169.254.0.0/16 is used for link-local addressing (APIPA). Option C is false because 192.168.0.0/16 is a private address. Option D is false because 10.0.0.0/8 is private. Option E is false because a /24 subnet mask provides 254 usable host addresses, not 256.
What should I do if I get this JNCIA-JUNOS question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related JNCIA-JUNOS subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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