LFCS Networking Practice Question
Network Topology
An administrator is unable to SSH into the server from a remote host at 192.168.1.100. Based on the exhibited iptables rules, what is the most likely reason?
⚠ Common exam trap
The trap here is that candidates see the INPUT chain policy is ACCEPT and assume all traffic is allowed, overlooking that a more specific rule (like the SSH rule with a source restriction) can prevent traffic from non-matching sources, effectively overriding the default policy for that service.
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
✓
The SSH rule only allows connections from 10.0.1.0/24, and 192.168.1.100 is not in that subnet
The exhibited iptables rules show an SSH rule that explicitly accepts incoming TCP traffic on port 22 only from the source subnet 10.0.1.0/24. The remote host at 192.168.1.100 is not within that subnet, so the SSH rule does not match, and the packet will fall through to the next rule or the default policy. Since no other rule permits SSH from 192.168.1.100, the connection is implicitly dropped or rejected, preventing SSH access.
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 SSH rule only allows connections from 10.0.1.0/24, and 192.168.1.100 is not in that subnet
Why this is correct
The second rule allows SSH only from 10.0.1.0/24, and the third rule drops all other SSH.
- ✗
SSH is not allowed from any source
Why it's wrong here
SSH is allowed from the local subnet.
- ✗
The INPUT chain policy is ACCEPT, so SSH should be allowed
Why it's wrong here
The explicit DROP rule overrides the default policy.
- ✗
The DROP rule for SSH is not matching because of packet count zero
Why it's wrong here
The packet count is zero because no packets have matched yet; it will match if traffic arrives.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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