The correct answer is that the ACL blocks SSH and RDP access to 192.168.1.100 from any source. This is because the ACL is applied inbound on GigabitEthernet0/0, meaning it evaluates traffic as it enters the interface, before any routing decision is made. The permit statement only allows traffic sourced from host 192.168.1.100 destined to the 10.0.0.0/24 network, so any other traffic—including SSH and RDP from any source to that server—is implicitly denied by the default deny rule at the end of the ACL. On the CompTIA SecurityX CAS-004 exam, this tests your understanding of ACL evaluation direction and the implicit deny, a common trap where candidates forget that inbound ACLs filter traffic before it reaches the destination. A frequent mistake is assuming the permit statement allows all traffic to or from the host, but it only applies to the specific source-destination pair. Remember: inbound ACLs check the source IP first, and if no explicit permit matches, the packet is dropped. A helpful memory tip is “Inbound checks the source, outbound checks the destination.”
CAS-004 Security Architecture Practice Question
This CAS-004 practice question tests your understanding of security architecture. 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.
Exhibit
Refer to the exhibit.
```
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip access-group ACL-IN in
!
interface GigabitEthernet0/1
ip address 10.0.0.1 255.255.255.0
!
access-list 100 deny tcp any host 192.168.1.100 eq 22
access-list 100 deny tcp any host 192.168.1.100 eq 3389
access-list 100 permit ip any any
```
A network administrator is troubleshooting connectivity to a server at 192.168.1.100. The ACL shown is applied inbound on GigabitEthernet0/0. Which THREE statements are true regarding this ACL configuration? (Choose three.)
Refer to the exhibit.
```
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip access-group ACL-IN in
!
interface GigabitEthernet0/1
ip address 10.0.0.1 255.255.255.0
!
access-list 100 deny tcp any host 192.168.1.100 eq 22
access-list 100 deny tcp any host 192.168.1.100 eq 3389
access-list 100 permit ip any any
```
A
The ACL will block all traffic from the 192.168.1.0/24 network to 10.0.0.0/24
Why wrong: The ACL permits all traffic; it does not block to 10.0.0.0/24. Also, it filters inbound on G0/0, not outbound.
B
Traffic sourced from 192.168.1.100 going to the 10.0.0.0/24 network will be permitted
The ACL does not filter traffic sourced from 192.168.1.100; it filters based on destination.
C
Traffic from the 10.0.0.0/24 network to 192.168.1.100 is not affected by this ACL
The ACL is applied inbound on G0/0; traffic from 10.0.0.0/24 enters via G0/1.
D
The implicit deny at the end of the ACL will block all other traffic not explicitly permitted
Why wrong: The explicit permit ip any any overrides the implicit deny for all traffic.
E
The ACL blocks SSH and RDP access to 192.168.1.100 from any source
The deny entries for port 22 and 3389 block these protocols.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Traffic sourced from 192.168.1.100 going to the 10.0.0.0/24 network will be permitted
Option B is correct because the ACL, when applied inbound on GigabitEthernet0/0, evaluates traffic entering the interface. The permit statement allows traffic sourced from host 192.168.1.100 destined to the 10.0.0.0/24 network, so that specific traffic is explicitly permitted.
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.
✗
The ACL will block all traffic from the 192.168.1.0/24 network to 10.0.0.0/24
Why it's wrong here
The ACL permits all traffic; it does not block to 10.0.0.0/24. Also, it filters inbound on G0/0, not outbound.
✓
Traffic sourced from 192.168.1.100 going to the 10.0.0.0/24 network will be permitted
Why this is correct
The ACL does not filter traffic sourced from 192.168.1.100; it filters based on destination.
Related concept
Read the scenario before looking for a memorised answer.
✓
Traffic from the 10.0.0.0/24 network to 192.168.1.100 is not affected by this ACL
Why this is correct
The ACL is applied inbound on G0/0; traffic from 10.0.0.0/24 enters via G0/1.
Related concept
Read the scenario before looking for a memorised answer.
✗
The implicit deny at the end of the ACL will block all other traffic not explicitly permitted
Why it's wrong here
The explicit permit ip any any overrides the implicit deny for all traffic.
✓
The ACL blocks SSH and RDP access to 192.168.1.100 from any source
Why this is correct
The deny entries for port 22 and 3389 block these protocols.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the direction of ACL application, assuming an inbound ACL on an interface affects traffic destined to that interface's IP address, when in fact it only filters traffic entering the interface from the outside.
Detailed technical explanation
How to think about this question
In Cisco IOS, ACLs are processed top-down with an implicit deny all at the end, and when applied inbound, they filter traffic before routing decisions are made. The permit statement uses a wildcard mask of 0.0.0.0 for the host, which is equivalent to the 'host' keyword, and the destination wildcard mask 0.0.0.255 matches the 10.0.0.0/24 network. Understanding the direction of ACL application is critical: inbound ACLs on an interface filter traffic coming into that interface, so traffic from the 10.0.0.0/24 network to 192.168.1.100 would be outbound on that interface and thus not evaluated by this ACL.
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.
Security Architecture — This question tests Security Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Traffic sourced from 192.168.1.100 going to the 10.0.0.0/24 network will be permitted — Option B is correct because the ACL, when applied inbound on GigabitEthernet0/0, evaluates traffic entering the interface. The permit statement allows traffic sourced from host 192.168.1.100 destined to the 10.0.0.0/24 network, so that specific traffic is explicitly permitted.
What should I do if I get this CAS-004 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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