The correct answer is that the ACL blocks traffic sourced from 10.0.0.0/8 entering G0/0, but allows all other traffic. This is because the ACL is applied inbound on the interface with a single explicit deny statement matching the 10.0.0.0/8 subnet, and every ACL ends with an implicit deny any, meaning any source IP not matching the deny rule is automatically permitted. On the Cisco SCOR / CCNP Security Core 350-701 exam, this tests your understanding of how an ACL effect blocking source subnet works, specifically that the implicit deny only applies to traffic not explicitly matched—a common trap is assuming the implicit deny blocks everything, when in fact it only blocks what isn’t already permitted or denied by earlier lines. A useful memory tip: “Explicit deny blocks the target; implicit deny catches the rest.”
350-701 Network Security Practice Question
This 350-701 practice question tests your understanding of network security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Exhibit
interface GigabitEthernet0/0
ip address 10.1.1.1 255.255.255.0
ip access-group INBOUND in
!
ip access-list extended INBOUND
deny ip 10.0.0.0 0.255.255.255 any
permit ip any any
!
interface Serial0/0/0
ip address 172.16.1.1 255.255.255.252
!
router eigrp 100
network 10.1.1.0 0.0.0.255
network 172.16.1.0 0.0.0.3
Refer to the exhibit. An engineer has configured the ACL on the GigabitEthernet0/0 interface. Which of the following is true about the effect of this ACL?
interface GigabitEthernet0/0
ip address 10.1.1.1 255.255.255.0
ip access-group INBOUND in
!
ip access-list extended INBOUND
deny ip 10.0.0.0 0.255.255.255 any
permit ip any any
!
interface Serial0/0/0
ip address 172.16.1.1 255.255.255.252
!
router eigrp 100
network 10.1.1.0 0.0.0.255
network 172.16.1.0 0.0.0.3
A
It blocks all IP traffic from entering G0/0 because of the deny statement.
Why wrong: The permit any any allows all traffic that is not denied.
B
It blocks traffic sourced from 10.0.0.0/8 entering G0/0, but allows other traffic.
The deny statement blocks source 10.0.0.0/8, and the permit any any allows all else.
C
It permits all traffic because the ACL is misconfigured.
Why wrong: The ACL is correctly configured and will block traffic from 10.0.0.0/8.
D
It blocks traffic destined to 10.0.0.0/8 entering G0/0, but allows other traffic.
Why wrong: The ACL filters on source address, not destination.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It blocks traffic sourced from 10.0.0.0/8 entering G0/0, but allows other traffic.
The ACL is applied inbound on GigabitEthernet0/0 with a single deny statement for source IP 10.0.0.0/8. Since ACLs have an implicit deny any at the end, traffic from the 10.0.0.0/8 range is blocked, but all other IP traffic is implicitly permitted because the explicit deny only matches that source range. This makes option B correct.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
It blocks all IP traffic from entering G0/0 because of the deny statement.
Why it's wrong here
The permit any any allows all traffic that is not denied.
✓
It blocks traffic sourced from 10.0.0.0/8 entering G0/0, but allows other traffic.
Why this is correct
The deny statement blocks source 10.0.0.0/8, and the permit any any allows all else.
Related concept
Read the scenario before looking for a memorised answer.
✗
It permits all traffic because the ACL is misconfigured.
Why it's wrong here
The ACL is correctly configured and will block traffic from 10.0.0.0/8.
✗
It blocks traffic destined to 10.0.0.0/8 entering G0/0, but allows other traffic.
Why it's wrong here
The ACL filters on source address, not destination.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a single deny statement in an ACL blocks all traffic, when in fact the implicit permit any allows all other traffic unless a permit any is explicitly omitted or the ACL is applied in a way that triggers the implicit deny.
Detailed technical explanation
How to think about this question
Standard and extended ACLs in Cisco IOS apply an implicit deny any at the end, but only if no permit statement exists; however, in this case, the single deny statement does not override the implicit permit for non-matching traffic because the ACL is not terminated with a permit any. Under the hood, ACLs are processed top-down, and the first match determines the action; if no match occurs, the implicit deny any would block all traffic, but here the implicit deny is actually an implicit permit because the ACL is used as a simple filter without a final permit statement—this is a common point of confusion. In real-world scenarios, engineers often forget to add a permit any statement, leading to unintended blocking of all traffic, but here the single deny only affects the specified source range.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: It blocks traffic sourced from 10.0.0.0/8 entering G0/0, but allows other traffic. — The ACL is applied inbound on GigabitEthernet0/0 with a single deny statement for source IP 10.0.0.0/8. Since ACLs have an implicit deny any at the end, traffic from the 10.0.0.0/8 range is blocked, but all other IP traffic is implicitly permitted because the explicit deny only matches that source range. This makes option B correct.
What should I do if I get this 350-701 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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