Practical setting of Linux Firewall iptables, linux Firewall iptables

Practical setting of Linux Firewall iptables, linux Firewall iptables

One important step to maintain a server is to manage the opening and closing of ports to prevent external malicious attacks from exploiting the ports occupied by these services.

First, you can view the iptables information:

Sudo iptables-L

Each rule is listed. The rule marked with ACCEPT indicates that the communication indicated by this rule can be successful, and the rule marked with DROP indicates that the communication indicated by this rule is blocked. Note that during system running, a rule will be matched from the beginning to the end. Therefore, the last rule is DROP, which indicates that the rule is finished, and no DROP is in the middle, otherwise, the subsequent ACCEPT does not work.

Add Rules:

# Iptables-a input-p tcp-I eth0 -- dport ssh-j ACCEPT

-A indicates append,-p tcp indicates tcp protocol,-I eth0 indicates Nic, -- dport ssh indicates port ssh (that is, 22), and-j ACCEPT indicates that this rule is ACCEPT. If we want to open port 9001, replace ssh with port 9001.

Delete rule:

# Iptables-d input 3

3 refers to the third rule, which is the table listed in iptables-L above. The first row is the first rule.

The last one is DROP, so we need to block communication:

# Iptables-a input-j DROP