- A
Add the established keyword to the ACL to permit return traffic for existing sessions.
The established keyword allows TCP return traffic that matches sessions originated from the internal network. It is the standard method to handle stateful return traffic with a stateless ACL.
- B
Add a new access-list entry permitting all traffic from internet hosts to the 10.0.0.0/8 network.
Why wrong: This would permit all inbound traffic from the internet to the internal network, creating a severe security risk. It also does not dynamically track sessions and is impractical for a large, unknown set of internet hosts.
- C
Remove the outbound ACL and apply a new inbound ACL on the same interface.
Why wrong: Changing the direction of the ACL does not solve the statelessness problem. An inbound ACL would still need to specifically allow return traffic, potentially requiring the same established mechanism or explicit permits. This action only moves the filtering point without addressing the root issue.
- D
Replace the ACL with a stateful firewall rule set.
Why wrong: While using a stateful firewall would inherently solve the issue, it is an overly drastic next step. The immediate, simple remedy is to modify the existing ACL with the established keyword, which is a valid and common workaround on Cisco IOS. Replacing the device or reengineering the security policy is premature.
Quick Answer
The answer is to add the established keyword to the ACL to permit return traffic for existing sessions. This is correct because extended ACLs are stateless, meaning they inspect each packet individually without tracking session state; when an outbound ACL permits traffic from the 10.0.0.0/8 network to the internet, the return packets from internet hosts are seen as new inbound traffic and are dropped unless explicitly allowed. The established keyword solves this by matching TCP packets with the ACK or RST bits set, which indicates they belong to an already initiated session, effectively allowing return traffic without opening the network to arbitrary inbound connections. On the CCNA 200-301 v2 exam, this scenario tests your understanding of the stateless nature of extended ACLs and the common trap of forgetting that outbound permit statements do not automatically permit return traffic. A useful memory tip is to think of the established keyword as the “ACK-nowledgment” filter—it only lets in packets that are responding to a conversation your router started.
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. 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.
A network technician applies an extended ACL outbound on the WAN interface Gi0/0 to block traffic from the 10.0.0.0/8 network to internet hosts. After applying the ACL, internal users report they cannot access any web pages because return traffic from internet hosts is being dropped. The technician verifies the ACL entries and finds only statements controlling outbound traffic. What is the most appropriate next action?
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
Add the established keyword to the ACL to permit return traffic for existing sessions.
Extended ACLs are stateless; they inspect each packet individually without tracking session state. When an outbound ACL permits outbound traffic from the inside network to the internet, the return traffic is not automatically allowed. The established keyword in a TCP access-list entry matches packets that have the ACK or RST bits set, indicating they belong to an established session. Adding this keyword to a permit statement for return traffic allows the router to dynamically permit responses to internally initiated connections without opening the network to all inbound traffic. This addresses the transport layer (Layer 4) state required for bidirectional communication.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Add the established keyword to the ACL to permit return traffic for existing sessions.
- ✗
Add a new access-list entry permitting all traffic from internet hosts to the 10.0.0.0/8 network.
Why it's wrong here
This would permit all inbound traffic from the internet to the internal network, creating a severe security risk. It also does not dynamically track sessions and is impractical for a large, unknown set of internet hosts.
- ✗
Remove the outbound ACL and apply a new inbound ACL on the same interface.
Why it's wrong here
Changing the direction of the ACL does not solve the statelessness problem. An inbound ACL would still need to specifically allow return traffic, potentially requiring the same established mechanism or explicit permits. This action only moves the filtering point without addressing the root issue.
- ✗
Replace the ACL with a stateful firewall rule set.
Why it's wrong here
While using a stateful firewall would inherently solve the issue, it is an overly drastic next step. The immediate, simple remedy is to modify the existing ACL with the established keyword, which is a valid and common workaround on Cisco IOS. Replacing the device or reengineering the security policy is premature.
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.
✓Add the established keyword to the ACL to permit return traffic for existing sessions.Correct answer▾
Why this is correct
The established keyword allows TCP return traffic that matches sessions originated from the internal network. It is the standard method to handle stateful return traffic with a stateless ACL.
✗Add a new access-list entry permitting all traffic from internet hosts to the 10.0.0.0/8 network.Wrong answer — click to see why▾
Why this is wrong here
Candidates assume that any missing traffic must be explicitly permitted, but this ignores the need for stateful inspection and leads to an overly permissive rule.
✗Remove the outbound ACL and apply a new inbound ACL on the same interface.Wrong answer — click to see why▾
Why this is wrong here
Candidates mistakenly think that moving the ACL to inbound direction will inherently permit return traffic because it inspects packets entering the interface, but the ACL still processes each packet individually without keeping state.
✗Replace the ACL with a stateful firewall rule set.Wrong answer — click to see why▾
Why this is wrong here
Candidates may think that only a stateful firewall can handle return traffic, overlooking the established keyword's capability to emulate stateful behavior for TCP traffic on an ACL.
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: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Keyword trap
While using a stateful firewall would inherently solve the issue, it is an overly drastic next step. The immediate, simple remedy is to modify the existing ACL with the established keyword, which is a valid and common workaround on Cisco IOS. Replacing the device or reengineering the security policy is premature.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 200-301 ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Add the established keyword to the ACL to permit return traffic for existing sessions. — Extended ACLs are stateless; they inspect each packet individually without tracking session state. When an outbound ACL permits outbound traffic from the inside network to the internet, the return traffic is not automatically allowed. The established keyword in a TCP access-list entry matches packets that have the ACK or RST bits set, indicating they belong to an established session. Adding this keyword to a permit statement for return traffic allows the router to dynamically permit responses to internally initiated connections without opening the network to all inbound traffic. This addresses the transport layer (Layer 4) state required for bidirectional communication.
What should I do if I get this 200-301 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 200-301 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jun 14, 2026
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