hardMultiple ChoiceObjective-mapped
CAS-004 Practice Question: A network administrator is troubleshooting…
Exhibit
Refer to the exhibit.
```
# iptables -L FORWARD -v -n
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- eth0 eth1 10.0.1.0/24 0.0.0.0/0 state NEW,ESTABLISHED
0 0 ACCEPT all -- eth1 eth0 0.0.0.0/0 10.0.1.0/24 state ESTABLISHED
```A network administrator is troubleshooting connectivity issues. Based on the exhibit, which of the following is true about the iptables rules?
⚠ Common exam trap
A common mix-up: candidates confuse the FORWARD chain with the INPUT chain, assuming that rules in the FORWARD chain apply to traffic destined for the firewall itself, or they overlook that the default policy for the FORWARD chain is DROP (not ACCEPT) unless explicitly set to ACCEPT in the exhibit.
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
✓
Traffic from 10.0.1.0/24 to the internet is allowed, but return traffic is only allowed if it is part of an established connection.
The iptables rules show a default FORWARD policy of DROP (as indicated by the 'policy DROP' line), which drops all traffic not explicitly allowed. The rule '-A FORWARD -s 10.0.1.0/24 -j ACCEPT' allows outbound traffic from the 10.0.1.0/24 subnet to the internet. The rule '-A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT' ensures that return traffic belonging to an existing connection is permitted back, while new inbound connections from the internet are implicitly dropped by the default DROP policy.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
New connections from the internet to 10.0.1.0/24 are allowed.
Why it's wrong here
Only established connections from internet to 10.0.1.0/24 are allowed; new connections are dropped.
- ✗
All traffic is allowed by default because the policy is ACCEPT.
Why it's wrong here
The policy is DROP, not ACCEPT.
- ✓
Traffic from 10.0.1.0/24 to the internet is allowed, but return traffic is only allowed if it is part of an established connection.
Why this is correct
The first rule matches new and established traffic from 10.0.1.0/24; the second matches only established traffic back.
- ✗
The rules apply to incoming traffic on the firewall itself.
Why it's wrong here
The FORWARD chain applies to traffic passing through the firewall, not traffic destined to the firewall.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CAS-005 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CAS-005 exam.