Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
Which statement best describes why the subnet mask is necessary even when DNS and the default gateway are configured correctly?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
Because the host still must determine local versus remote scope before deciding how to send traffic.
This is correct because the subnet mask drives local-versus-remote decision making.
B
Distractor review
Because the subnet mask is what resolves hostnames into IP addresses.
This is wrong because DNS resolves names, not subnet masks.
C
Distractor review
Because the subnet mask replaces the default gateway for all remote traffic.
This is wrong because remote traffic still relies on the gateway.
D
Distractor review
Because the subnet mask is required only by switches, not hosts.
This is wrong because hosts use subnet masks directly.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is assuming that the subnet mask is unnecessary if DNS and the default gateway are configured correctly. Candidates might mistakenly think DNS handles all addressing or that the default gateway automatically manages all traffic routing. However, the subnet mask is critical for the host to determine whether a destination IP is local or remote before deciding to send traffic directly or via the gateway. Overlooking this leads to misunderstanding how IP routing decisions are made at the host level.
Technical deep dive
How to think about this question
The subnet mask is a fundamental component of IP networking that defines the network and host portions of an IP address. It enables a device to determine which IP addresses are within its local subnet and which are outside, requiring routing. This distinction is crucial because it dictates how traffic is forwarded—either directly on the local network or via a router. Without the subnet mask, a host cannot accurately identify the scope of an IP address, making communication inefficient or impossible. When a host wants to send traffic, it first compares the destination IP address with its own IP address and subnet mask. This comparison determines whether the destination is local or remote. If local, the host sends traffic directly using Layer 2 addressing. If remote, the host forwards the traffic to the default gateway, which routes it beyond the local subnet. This decision process is independent of DNS or default gateway configuration; DNS resolves names to IP addresses, and the gateway forwards remote traffic, but neither replaces the subnet mask’s role in local-versus-remote determination. A common exam trap is to confuse the subnet mask’s role with DNS or default gateway functions. Some may incorrectly believe the subnet mask resolves hostnames or replaces the gateway for remote traffic. In practice, the subnet mask is essential for the host’s initial routing decision. Without it, even with DNS and a gateway configured, the host cannot decide how to send packets properly, leading to communication failures or misrouted traffic.
KKey Concepts to Remember
- The subnet mask defines the network and host portions of an IP address, enabling hosts to identify local versus remote destinations.
- A host uses the subnet mask to determine whether to send traffic directly on the local subnet or forward it to the default gateway.
- DNS resolves domain names to IP addresses but does not influence how a host determines local or remote traffic scope.
- The default gateway forwards traffic destined for remote networks but relies on the host’s subnet mask decision to receive that traffic.
- Without the subnet mask, a host cannot correctly decide the scope of an IP address, causing communication failures even if DNS and gateway are configured.
- Subnetting logic is fundamental to IP routing and is processed locally by the host before any routing or name resolution occurs.
- Hosts use subnet masks directly to perform routing decisions, while switches do not require subnet masks for basic Layer 2 forwarding.
- The subnet mask drives the initial routing decision on the host, which is essential for proper network communication and traffic delivery.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Related practice questions
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
The subnet mask defines the network and host portions of an IP address, enabling hosts to identify local versus remote destinations.
What is the correct answer to this question?
The correct answer is: Because the host still must determine local versus remote scope before deciding how to send traffic. — The subnet mask is still necessary because the host must decide whether a destination is local or remote before it knows whether to send directly or use the gateway. In practical terms, DNS may help turn names into IP addresses and the default gateway may help with remote delivery, but the host still needs its subnet logic to choose the right behavior. This is a good medium-level foundational question because it connects several host configuration elements without confusing their roles.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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