![]() This means that the first rule has no effect. The first rule blocks traffic from the 192.168.0.0/24 network, then the rule below allows traffic from the 192.168.0.0/16 network. Here is an example of the wrong order: # iptables -A FORWARD -s 192.168.0.0/24 -j DROP # iptables -A FORWARD -s 192.168.0.0/16 -j ACCEPT Every firewall applies rules from the top to down. This is the most important feature, because if you are not aware of it, you can make mistakes. The rule above restricts access to Google’s public DNS. Here is an example: # iptables -A OUTPUT -d 8.8.8.8 -dport 53 -p udp -m udp -j DROP You can filter by source IP address, destination IP address, source port, destination port, protocol, and so on. There are many criteria for creating filtering rules. Linux main firewall is iptables (or modern replacement notables), which is a part of a netfilter project. This means you can block some traffic and allow some others to go. This is the main function of the firewall, this is what the firewall was created for. They are very useful not only for network engineers, but for any IT engineer. ![]() ![]() ![]() Photo By Lewis Kang’ethe Ngugi, firewall has many functions you probably don’t know about. ![]()
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