- A
NTP authentication with MD5 keys
Authentication verifies the identity of the NTP server.
- B
NTP symmetric active mode
Why wrong: Symmetric mode is for peering, not security.
- C
NTP broadcast client mode
Why wrong: Broadcast mode does not authenticate the server.
- D
NTP access group with read-only community
Why wrong: Access groups restrict access but do not authenticate.
Question 548 of 1,000
350-501 Security and Services Practice Question
This 350-501 practice question tests your understanding of security and services. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
To secure NTP in a service provider network, which feature should be enabled on IOS XR routers to prevent time synchronization with unauthorized NTP servers?
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
✓
NTP authentication with MD5 keys
NTP authentication ensures that the router only synchronizes with trusted servers that have the correct key. Access lists can also limit, but authentication provides cryptographic verification. NTP broadcast mode is less secure; symmetric mode is for peer-to-peer.
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.
- ✓
NTP authentication with MD5 keys
- ✗
NTP symmetric active mode
Why it's wrong here
Symmetric mode is for peering, not security.
- ✗
NTP broadcast client mode
Why it's wrong here
Broadcast mode does not authenticate the server.
- ✗
NTP access group with read-only community
Why it's wrong here
Access groups restrict access but do not authenticate.
Common exam traps
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.
Visual reference
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 350-501 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this 350-501 question test?
Security and Services — This question tests Security and Services — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: NTP authentication with MD5 keys — NTP authentication ensures that the router only synchronizes with trusted servers that have the correct key. Access lists can also limit, but authentication provides cryptographic verification. NTP broadcast mode is less secure; symmetric mode is for peer-to-peer.
What should I do if I get this 350-501 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 350-501 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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Last reviewed: Jul 4, 2026
This 350-501 practice question is part of Courseiva's free Cisco 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 350-501 exam.
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