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

The `iptables -L` command lists all current firewall rules in all chains. Adding -v gives verbose output and -n prevents DNS lookups.

Question 2

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

Accepted Answer

INPUT

Answer

The INPUT chain processes packets that are destined for the local machine itself, not forwarded to another host.

Question 3

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

Accepted Answer

Silently discards matching packets

Answer

DROP silently discards packets without notifying the sender, unlike REJECT which sends an error message back.

Question 4

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

Accepted Answer

firewalld

Answer

firewalld is the default dynamic firewall daemon used on RHEL/CentOS/Fedora systems, providing a zone-based interface to netfilter.

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

The correct syntax uses --add-port=443/tcp with --permanent to persist the rule across reboots, followed by --reload to apply it.

Linux Practice Test