LFCS Networking Practice Question
Which THREE are built-in chains in the iptables filter table? (Choose three.)
⚠ Common exam trap
Watch out — candidates often confuse the filter table's chains with those of the nat table (PREROUTING, POSTROUTING) because all chains are used in packet traversal, but only INPUT, OUTPUT, and FORWARD belong to the filter table.
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
✓
INPUT
The filter table in iptables is used for packet filtering decisions based on IP addresses, ports, and protocols. Its built-in chains are INPUT (for packets destined for the local system), OUTPUT (for packets originating from the local system), and FORWARD (for packets routed through the system). These three chains allow you to control traffic at different points in the packet flow.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
POSTROUTING
Why it's wrong here
POSTROUTING is in the nat and mangle tables, not filter.
- ✓
INPUT
Why this is correct
INPUT chain processes incoming packets destined for the local system.
- ✓
OUTPUT
Why this is correct
OUTPUT chain processes outgoing packets from the local system.
- ✓
FORWARD
Why this is correct
FORWARD chain processes packets routed through the system.
- ✗
PREROUTING
Why it's wrong here
PREROUTING is in the nat and mangle tables, not filter.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.