- A
Fragment it anyway and forward the pieces
Why wrong: The router cannot simply ignore the Don't Fragment bit. That bit exists specifically to prevent fragmentation. If the router fragmented the packet anyway, it would violate the sender's requirement and defeat the whole point of the flag.
- B
Drop it and typically return an ICMP message indicating fragmentation is needed
Correct. This is correct. When a packet is too large for the outgoing MTU and fragmentation is not allowed, the router drops the packet and usually informs the sender that fragmentation would be required.
- C
Translate it to IPv6 and forward it
Why wrong: Routers do not solve an oversized IPv4 packet by converting it into IPv6. These are different protocols with different headers and forwarding behaviors. The issue here is MTU and fragmentation policy, not an opportunity for protocol conversion.
- D
Broadcast it so another router can handle fragmentation
Why wrong: Routers do not broadcast oversized packets to let another router solve the problem. The forwarding decision is made locally. If the packet cannot be forwarded because of the MTU and DF setting, it is dropped.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: the Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances.. 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.
A host sends a packet larger than the outgoing interface MTU, and the IPv4 header has the Don't Fragment bit set.
What will a router do with the packet?
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
Drop it and typically return an ICMP message indicating fragmentation is needed
The router drops the packet because the packet is too large for the next link and the sender has explicitly said the packet must not be fragmented. In IPv4, the Don't Fragment bit tells routers not to break the packet into smaller pieces. If the outgoing interface MTU is smaller than the packet size, the router cannot legally forward it as-is and cannot fragment it, so the normal result is to drop the packet and usually send back an ICMP unreachable message indicating that fragmentation is needed. In plain terms, the router is telling the sender, 'This packet is too big for the path you chose, and you told me I am not allowed to split it.' This behavior is central to path MTU discovery.
Key principle: The Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Fragment it anyway and forward the pieces
Why it's wrong here
The router cannot simply ignore the Don't Fragment bit. That bit exists specifically to prevent fragmentation. If the router fragmented the packet anyway, it would violate the sender's requirement and defeat the whole point of the flag.
When this WOULD be correct
In a different scenario where a packet is received without the Don't Fragment bit set and exceeds the MTU, a router could fragment it into smaller packets to fit the MTU size and forward the fragments accordingly. This would be a valid situation for option A to be correct.
- ✓
Drop it and typically return an ICMP message indicating fragmentation is needed
Why this is correct
Correct. This is correct. When a packet is too large for the outgoing MTU and fragmentation is not allowed, the router drops the packet and usually informs the sender that fragmentation would be required.
Related concept
The Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances.
- ✗
Translate it to IPv6 and forward it
Why it's wrong here
Routers do not solve an oversized IPv4 packet by converting it into IPv6. These are different protocols with different headers and forwarding behaviors. The issue here is MTU and fragmentation policy, not an opportunity for protocol conversion.
When this WOULD be correct
In a different scenario where a question asks about a router's behavior when handling a packet that is too large but does not have the Don't Fragment bit set, translating the packet to IPv6 could be a valid option if the router supports IPv6 and is configured to perform such translations.
- ✗
Broadcast it so another router can handle fragmentation
Why it's wrong here
Routers do not broadcast oversized packets to let another router solve the problem. The forwarding decision is made locally. If the packet cannot be forwarded because of the MTU and DF setting, it is dropped.
When this WOULD be correct
In a different scenario where the question states that the packet is allowed to be fragmented, a router might broadcast the packet to other routers in a network that supports fragmentation to handle oversized packets collectively. This could occur in a network with specific configurations allowing such behavior.
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.
✓Drop it and typically return an ICMP message indicating fragmentation is neededCorrect answer▾
Why this is correct
Correct. This is correct. When a packet is too large for the outgoing MTU and fragmentation is not allowed, the router drops the packet and usually informs the sender that fragmentation would be required.
✗Fragment it anyway and forward the piecesWrong answer — click to see why▾
Why this is wrong here
The router cannot fragment the packet because the Don't Fragment (DF) bit is set. Fragmentation would violate the sender's explicit instruction and is not permitted by the IPv4 specification.
★ When this WOULD be the correct answer
In a different scenario where a packet is received without the Don't Fragment bit set and exceeds the MTU, a router could fragment it into smaller packets to fit the MTU size and forward the fragments accordingly. This would be a valid situation for option A to be correct.
Why candidates choose this
Students may think that routers always fragment oversized packets as a normal forwarding behavior, overlooking the DF bit's role in preventing fragmentation.
✗Translate it to IPv6 and forward itWrong answer — click to see why▾
Why this is wrong here
IPv4-to-IPv6 translation is not a mechanism to handle MTU issues; it is used for interoperability between IPv4 and IPv6 networks. The router does not perform protocol translation to solve a fragmentation problem.
★ When this WOULD be the correct answer
In a different scenario where a question asks about a router's behavior when handling a packet that is too large but does not have the Don't Fragment bit set, translating the packet to IPv6 could be a valid option if the router supports IPv6 and is configured to perform such translations.
Why candidates choose this
Students might confuse the concept of protocol translation with a general 'fix-all' solution, or think that IPv6's larger MTU could bypass the issue, but the packet remains IPv4 and translation is unrelated.
✗Broadcast it so another router can handle fragmentationWrong answer — click to see why▾
Why this is wrong here
Routers do not broadcast packets to offload fragmentation to another router. The forwarding decision is made locally; if the packet cannot be forwarded due to MTU constraints and DF set, it is dropped immediately.
★ When this WOULD be the correct answer
In a different scenario where the question states that the packet is allowed to be fragmented, a router might broadcast the packet to other routers in a network that supports fragmentation to handle oversized packets collectively. This could occur in a network with specific configurations allowing such behavior.
Why candidates choose this
Students may incorrectly believe that broadcasting can help find a router with a larger MTU, but broadcasting is not used for unicast forwarding and does not resolve the fragmentation issue.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common exam trap is to assume that routers will fragment any oversized IPv4 packet regardless of the Don't Fragment bit. Candidates might select the option that routers fragment the packet anyway, ignoring the DF bit. This is incorrect because the DF bit explicitly prevents fragmentation. Another tempting mistake is to think that routers might broadcast the packet to other routers or convert it to IPv6 to solve the problem, which does not happen. Understanding that the router must drop the packet and send an ICMP message is critical to avoid this trap.
Detailed technical explanation
How to think about this question
IPv4 packets include a header flag called the Don't Fragment (DF) bit, which instructs routers along the path not to fragment the packet under any circumstances. Fragmentation is the process of breaking a large IP packet into smaller pieces so that each piece fits within the Maximum Transmission Unit (MTU) size of the outgoing interface. The MTU is the largest packet size that a network link can transmit without needing fragmentation. When a packet exceeds the MTU of the next hop, routers typically fragment the packet to ensure delivery. However, when the DF bit is set, routers are prohibited from fragmenting the packet. If the packet size exceeds the MTU of the outgoing interface, the router must drop the packet and send an ICMP Type 3 Code 4 message (Destination Unreachable, Fragmentation Needed and DF Set) back to the sender. This behavior is fundamental to Path MTU Discovery (PMTUD), a mechanism that allows the sender to learn the smallest MTU along the path and adjust packet sizes accordingly to avoid fragmentation. A common exam trap is to assume that routers will fragment packets regardless of the DF bit setting. This is incorrect because the DF bit explicitly forbids fragmentation. Another misconception is that routers might broadcast or convert the packet to IPv6 to solve the issue, which is not true. In practice, the router drops the packet and notifies the sender, prompting the sender to reduce packet size. This mechanism ensures efficient network operation and prevents fragmentation-related performance issues.
KKey Concepts to Remember
- The Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances.
- Routers compare the packet size against the outgoing interface MTU to decide if fragmentation is needed.
- If the packet exceeds the MTU and the DF bit is set, the router drops the packet and sends an ICMP fragmentation-needed message to the sender.
- Path MTU Discovery relies on the DF bit and ICMP messages to dynamically determine the smallest MTU along the path.
- Routers do not fragment packets when the DF bit is set, preserving the sender's requirement to avoid fragmentation.
- Routers do not convert IPv4 packets to IPv6 or broadcast oversized packets to other routers for fragmentation.
- ICMP Type 3 Code 4 messages inform the sender that fragmentation is required but prohibited by the DF bit.
- Dropping packets with the DF bit set and sending ICMP messages helps maintain efficient routing and avoids fragmentation overhead.
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.
Key takeaway
The Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances., then practise related 200-301 questions on the same topic to reinforce the concept.
- →
Network Services and Security — study guide chapter
Learn the concepts, then practise the questions
- →
Network Services and Security practice questions
Targeted practice on this topic area only
- →
All 200-301 questions
1,819 questions across all exam domains
- →
CCNA 200-301 v2 study guide
Full concept coverage aligned to exam objectives
- →
200-301 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Network Infrastructure and Connectivity practice questions
Practise 200-301 questions linked to Network Infrastructure and Connectivity.
Switching and Network Access practice questions
Practise 200-301 questions linked to Switching and Network Access.
IP Routing practice questions
Practise 200-301 questions linked to IP Routing.
Network Services and Security practice questions
Practise 200-301 questions linked to Network Services and Security.
AI and Network Operations practice questions
Practise 200-301 questions linked to AI and Network Operations.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
Practice this exam
Start a free 200-301 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — The Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances..
What is the correct answer to this question?
The correct answer is: Drop it and typically return an ICMP message indicating fragmentation is needed — The router drops the packet because the packet is too large for the next link and the sender has explicitly said the packet must not be fragmented. In IPv4, the Don't Fragment bit tells routers not to break the packet into smaller pieces. If the outgoing interface MTU is smaller than the packet size, the router cannot legally forward it as-is and cannot fragment it, so the normal result is to drop the packet and usually send back an ICMP unreachable message indicating that fragmentation is needed. In plain terms, the router is telling the sender, 'This packet is too big for the path you chose, and you told me I am not allowed to split it.' This behavior is central to path MTU discovery.
What should I do if I get this 200-301 question wrong?
Review the Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
The Don't Fragment (DF) bit in the IPv4 header instructs routers not to fragment the packet under any circumstances.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: May 17, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.