iptables: Linux firewall rules for a basic Web Server
What is iptables?
iptables
Firewall & iptables basics
Rules are first come first serve
In iptables much like other (but not all) firewall filtering packages the rules are presented in a list. When a packet is being processed, iptables will read through its rule-set list and the first rule that matches this packet completely gets applied.
For example if our rule-set looks like below, all HTTP connections will be denied:
- Allow all SSH Connections
- Deny all connections
- Allow all HTTP Connections
If the packet was for SSH it would be allowed because it matches rule #1, HTTP traffic on the other hand would be denied because it matches both rule #2 and rule #3. Because rule #2 says Deny all connections the HTTP traffic would be denied.
This is an example of why order matters with iptables, keep this in mind as we will see this later in this article.
