CCNA Network Services and Security Practice Question
Exhibit
Client output: IP address: 192.168.50.22/24 Default gateway: 192.168.50.1 DNS server: 0.0.0.0
Users receive addresses from the correct subnet and can reach destinations by IP address, but they cannot browse by hostname.
⚠ Common exam trap
Don't confuse general network connectivity options with DNS-specific configurations. Focus on what each DHCP option actually configures.
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
✓
DNS server option
If clients get an IP address and default gateway but cannot resolve names, the usual problem is the DNS server information handed out by DHCP. Without that, hostname lookups fail even though IP connectivity may still exist.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Default-router option
Why it's wrong here
The default-router option supplies the gateway IP address for traffic destined outside the local subnet. If it were missing, clients would be unable to route packets to remote networks, but this would not prevent hostname resolution when the DNS server is on the same Layer 3 segment. Because the symptom is specifically that users 'receive addresses from the correct subnet' yet fail name resolution, an absent gateway would cause a broader connectivity outage, not a DNS-specific malfunction.
When this WOULD be correct
In a different scenario where users cannot access external networks or specific services, but can resolve hostnames, the Default-router option could be missing or incorrect, leading to connectivity issues outside the local subnet.
- ✓
DNS server option
Why this is correct
The DHCP DNS-server option (option 6) provides clients with the IP address of a resolver to use for hostname-to-IP translation. When users receive a valid IP/prefix but no correct DNS server, name resolution fails even though all local network settings appear normal. Without a reachable DNS server, clients cannot resolve domain names, causing web and application connectivity failures while direct IP-based access still works.
- ✗
Lease time option
Why it's wrong here
The lease time option defines how long an IP address assignment is valid, after which the client must renew or rebind its lease. It is unrelated to the DNS resolver configuration; a shorter or longer lease only affects DHCP renewal frequency and address availability. If the lease expires without renewal the client simply obtains a new configuration, and the DNS server settings would still be provided at that time.
When this WOULD be correct
If the question were about a DHCP configuration issue where clients were unable to maintain their IP addresses or frequently lost connectivity, then a missing or incorrect lease time option could be the cause, making this answer correct.
- ✗
TFTP server option
Why it's wrong here
The TFTP server option is used to direct clients to a trivial FTP server, commonly for network bootstrapping, IP phone provisioning, or Cisco device configuration backup. It has no role in the Domain Name System or in resolving fully qualified domain names to IP addresses. Supplying a wrong or missing TFTP server would not affect DNS lookups; it would instead impede services that rely on TFTP-based file retrieval.
When this WOULD be correct
In a different scenario where users are unable to download configuration files or firmware updates from a TFTP server, the question might ask which DHCP option is missing. In that case, if the TFTP server option is not provided, it would be the correct answer.
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 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓DNS server optionCorrect answer▾
Why this is correct
The DHCP DNS-server option (option 6) provides clients with the IP address of a resolver to use for hostname-to-IP translation. When users receive a valid IP/prefix but no correct DNS server, name resolution fails even though all local network settings appear normal. Without a reachable DNS server, clients cannot resolve domain names, causing web and application connectivity failures while direct IP-based access still works.
✗Default-router optionWrong answer — click to see why▾
Why this is wrong here
The default-router option (option 3) provides the gateway for off-subnet traffic. While a missing gateway would prevent access to external networks, the scenario states users receive correct subnet addresses and can likely reach local resources. The inability to browse by hostname points to a DNS issue, not a routing problem.
★ When this WOULD be the correct answer
In a different scenario where users cannot access external networks or specific services, but can resolve hostnames, the Default-router option could be missing or incorrect, leading to connectivity issues outside the local subnet.
Why candidates choose this
Test-takers often associate internet browsing with a default gateway, assuming that if hostname resolution fails, it might be due to lack of internet connectivity. However, the question specifies that users cannot browse by hostname, which is a DNS function, not a routing one.
✗Lease time optionWrong answer — click to see why▾
Why this is wrong here
The lease time option (option 51) determines how long a client can use an assigned IP address before renewing. It does not affect DNS resolution or hostname browsing. A missing or incorrect lease time would cause IP address expiration issues, not name resolution failures.
★ When this WOULD be the correct answer
If the question were about a DHCP configuration issue where clients were unable to maintain their IP addresses or frequently lost connectivity, then a missing or incorrect lease time option could be the cause, making this answer correct.
Why candidates choose this
Students may confuse lease time with other DHCP options that affect network functionality, or they might think that a short lease could cause intermittent connectivity that impacts DNS. However, lease time is unrelated to DNS resolution.
✗TFTP server optionWrong answer — click to see why▾
Why this is wrong here
The TFTP server option (option 66) is used for booting devices like IP phones or diskless workstations to download configuration files or operating systems. It is not involved in hostname resolution. A missing TFTP server would not affect DNS lookups.
★ When this WOULD be the correct answer
In a different scenario where users are unable to download configuration files or firmware updates from a TFTP server, the question might ask which DHCP option is missing. In that case, if the TFTP server option is not provided, it would be the correct answer.
Why candidates choose this
Students may confuse TFTP with DNS because both are UDP-based services, or they might think that TFTP is needed for some name resolution process. However, TFTP has no role in DNS resolution.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Related to this question
Learn chapter
Configuring AAA with TACACS+ and RADIUS on IOS XE
Key term
Default gateway
A default gateway is a network device, typically a router, that acts as the exit point for traffic from a local network to other networks, including the internet.
Key term
Name Server
A name server is a specialized server that translates human-readable domain names into machine-readable IP addresses so that computers can find each other on a network.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.