Linux Firewall and Network Security

Question 1

Which command is used to list all current iptables rules in a Linux system?

Accepted Answer

iptables -L

Answer

iptables --show

Answer

iptables -list

Answer

iptables -display

Question 2

In iptables, which chain handles packets destined for the local system?

Accepted Answer

INPUT

Answer

OUTPUT

Answer

FORWARD

Answer

PREROUTING

Question 3

What does the `-j DROP` option do in an iptables rule?

Accepted Answer

Silently discards matching packets

Answer

Sends a rejection notice to the sender

Answer

Logs the packet and drops it

Answer

Forwards the packet to another chain

Question 4

Which firewall tool is the default frontend for managing netfilter on modern systemd-based Linux distributions?

Accepted Answer

firewalld

Answer

iptables

Answer

ufw

Answer

nftables

Question 5

What command allows you to add a permanent rule in firewalld to open port 443/tcp in the public zone?

Accepted Answer

firewall-cmd --zone=public --add-port=443/tcp --permanent

Answer

firewall-cmd --add-port=443 --zone=public

Answer

firewall-cmd --open=443/tcp --permanent

Answer

firewall-cmd --zone=public --port=443 --enable

Question 6

Which nftables command lists all current rules and tables?

Accepted Answer

nft list ruleset

Answer

nft show rules

Answer

nft -L

Answer

nft display all

Question 7

What is the purpose of the UFW (Uncomplicated Firewall) command `ufw enable`?

Accepted Answer

Activates the firewall and enables it to start on boot

Answer

Only enables the firewall for the current session

Answer

Reloads the firewall rules without enabling it

Answer

Creates a default allow-all policy

Question 8

In iptables, what does the `-m state --state ESTABLISHED,RELATED` match condition do?

Accepted Answer

Matches packets that are part of or related to an existing connection

Answer

Matches only new connection attempts

Answer

Matches all UDP packets regardless of state

Answer

Matches packets in the INVALID state only

Question 9

Which command would you use to block all incoming traffic from IP address 203.0.113.5?

Accepted Answer

iptables -A INPUT -s 203.0.113.5 -j DROP

Answer

iptables -A INPUT -d 203.0.113.5 -j DROP

Answer

iptables -B INPUT -s 203.0.113.5 -j DROP

Answer

iptables -BLOCK -s 203.0.113.5

Question 10

What does the `ss -tuln` command show?

Accepted Answer

All TCP and UDP listening sockets with numeric addresses

Answer

Active SSH tunnels only

Answer

Network interface statistics

Answer

Routing table entries