The answer is that all traffic from the internet to the internal network is denied. This is correct because firewall rule order is interpreted sequentially from top to bottom, and the first matching rule determines the action; here, the initial "deny any" rule for the entire 10.0.0.0/8 subnet blocks all traffic to that range, so the subsequent "permit" rule for 10.0.0.5 is never evaluated. On the CISM exam, this tests your understanding of implicit versus explicit deny and the critical concept that a broad deny rule placed before a specific permit rule renders the permit unreachable—a common trap where candidates mistakenly think a later permit overrides an earlier deny. To avoid this, remember the "first match wins" principle: always read firewall rules from top to bottom, and if a deny any covers the destination, no later permit can save it. A useful memory tip is "Deny first, permit last—or your traffic won't pass."
CISM Information Security Program Practice Question
This CISM practice question tests your understanding of information security program. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Exhibit:
```
access-list 100 deny ip any 10.0.0.0 0.255.255.255
access-list 100 permit tcp 192.168.1.0 0.0.0.255 host 10.0.0.5 eq 80
access-list 100 deny ip any any
```
The ACL is applied inbound on the external interface of the border router.
Based on the exhibit, which of the following is true about traffic from the internet to the internal network 10.0.0.0/8?
Refer to the exhibit.
Exhibit:
```
access-list 100 deny ip any 10.0.0.0 0.255.255.255
access-list 100 permit tcp 192.168.1.0 0.0.0.255 host 10.0.0.5 eq 80
access-list 100 deny ip any any
```
The ACL is applied inbound on the external interface of the border router.
A
Internet traffic to 10.0.0.5 is permitted only if from 192.168.1.0/24.
Why wrong: The deny rule blocks all, and source 192.168.1.0/24 is internal, not internet.
B
All traffic from the internet to the internal network is denied.
First rule denies all IP traffic to 10.0.0.0/8.
C
Traffic from the internet to 10.0.0.5 port 80 is permitted.
Why wrong: The earlier deny rule blocks all traffic to 10.0.0.0/8; permit is never evaluated.
D
Traffic from 192.168.1.0/24 to 10.0.0.5 port 80 is permitted.
Why wrong: That source is internal; ACL on external interface doesn't apply to internal traffic.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
All traffic from the internet to the internal network is denied.
The first deny rule blocks all IP traffic to 10.0.0.0/8 from any source, including internet. The permit only allows specific source, but it is after a deny any to 10.0.0.0/8, so traffic to 10.0.0.5 is also blocked? Actually, order matters: first deny any to 10.0.0.0/8 blocks all traffic to that network, then permit specific to 10.0.0.5 would never be reached. So internet traffic to internal is denied entirely.
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.
✗
Internet traffic to 10.0.0.5 is permitted only if from 192.168.1.0/24.
Why it's wrong here
The deny rule blocks all, and source 192.168.1.0/24 is internal, not internet.
✓
All traffic from the internet to the internal network is denied.
Why this is correct
First rule denies all IP traffic to 10.0.0.0/8.
Related concept
Standard ACLs match source addresses.
✗
Traffic from the internet to 10.0.0.5 port 80 is permitted.
Why it's wrong here
The earlier deny rule blocks all traffic to 10.0.0.0/8; permit is never evaluated.
✗
Traffic from 192.168.1.0/24 to 10.0.0.5 port 80 is permitted.
Why it's wrong here
That source is internal; ACL on external interface doesn't apply to internal traffic.
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.
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 CISM ACL questions on filtering logic and placement.
Information Security Program — This question tests Information Security Program — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: All traffic from the internet to the internal network is denied. — The first deny rule blocks all IP traffic to 10.0.0.0/8 from any source, including internet. The permit only allows specific source, but it is after a deny any to 10.0.0.0/8, so traffic to 10.0.0.5 is also blocked? Actually, order matters: first deny any to 10.0.0.0/8 blocks all traffic to that network, then permit specific to 10.0.0.5 would never be reached. So internet traffic to internal is denied entirely.
What should I do if I get this CISM 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 CISM ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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