This CAS-004 practice question tests your understanding of security architecture. 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
Refer to the exhibit.
```
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip access-group OUTSIDE_IN in
!
ip access-list extended OUTSIDE_IN
permit tcp any host 192.168.1.100 eq 80
permit tcp any host 192.168.1.100 eq 443
deny ip any any log
!
interface GigabitEthernet0/1
ip address 10.0.0.1 255.255.255.0
ip access-group INSIDE_OUT out
!
ip access-list extended INSIDE_OUT
permit ip 10.0.0.0 0.0.0.255 any
deny ip any any log
```
A security architect reviews this Cisco router ACL configuration. The web server at 192.168.1.100 is accessible from the internet. What additional security measure should be implemented to protect the internal network (10.0.0.0/24)?
Refer to the exhibit.
```
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip access-group OUTSIDE_IN in
!
ip access-list extended OUTSIDE_IN
permit tcp any host 192.168.1.100 eq 80
permit tcp any host 192.168.1.100 eq 443
deny ip any any log
!
interface GigabitEthernet0/1
ip address 10.0.0.1 255.255.255.0
ip access-group INSIDE_OUT out
!
ip access-list extended INSIDE_OUT
permit ip 10.0.0.0 0.0.0.255 any
deny ip any any log
```
A
Remove the log statement from the deny rules to improve performance
Why wrong: Removing logging reduces visibility without improving security; logging is important for monitoring.
B
Add an ACL on GigabitEthernet0/1 to limit outbound traffic to web ports only
Why wrong: Limiting outbound to web ports may be too restrictive and not address all threats; stateful firewall is better.
C
Replace the ACLs with a stateful firewall that inspects connection states
A stateful firewall provides deeper inspection and can prevent various attacks.
D
Apply the same OUTSIDE_IN ACL to GigabitEthernet0/1 inbound
Why wrong: This would block all incoming traffic, including legitimate internal traffic, and is not appropriate.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Replace the ACLs with a stateful firewall that inspects connection states
The INSIDE_OUT ACL allows all traffic from the internal network to any destination, including potentially malicious outbound connections. Implementing a stateful firewall would track connection states and provide better inspection. Egress filtering could be added, but stateful inspection is more comprehensive. The OUTSIDE_IN ACL only allows inbound web traffic, which is good. The missing piece is stateful awareness to prevent internal hosts from initiating connections to malicious external hosts.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Remove the log statement from the deny rules to improve performance
Why it's wrong here
Removing logging reduces visibility without improving security; logging is important for monitoring.
✗
Add an ACL on GigabitEthernet0/1 to limit outbound traffic to web ports only
Why it's wrong here
Limiting outbound to web ports may be too restrictive and not address all threats; stateful firewall is better.
✓
Replace the ACLs with a stateful firewall that inspects connection states
Why this is correct
A stateful firewall provides deeper inspection and can prevent various attacks.
Related concept
Static NAT maps one inside address to one outside address.
✗
Apply the same OUTSIDE_IN ACL to GigabitEthernet0/1 inbound
Why it's wrong here
This would block all incoming traffic, including legitimate internal traffic, and is not appropriate.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CAS-004 NAT questions on configuration and troubleshooting.
Security Architecture — This question tests Security Architecture — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Replace the ACLs with a stateful firewall that inspects connection states — The INSIDE_OUT ACL allows all traffic from the internal network to any destination, including potentially malicious outbound connections. Implementing a stateful firewall would track connection states and provide better inspection. Egress filtering could be added, but stateful inspection is more comprehensive. The OUTSIDE_IN ACL only allows inbound web traffic, which is good. The missing piece is stateful awareness to prevent internal hosts from initiating connections to malicious external hosts.
What should I do if I get this CAS-004 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CAS-004 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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