Opening a port on CentOS
CentOS 6
For example, if you want to open port 80,
iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
In the above example, "--dport 80" signifies the port number to be opened, replacing 80 with another port number opens that port, for example, if we wish to open port 8080,
iptables -A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT
iptables-save
service iptables restart
CentOS 7 / AlmaLinux 8 & 9 / Rocky Linux 8 & 9
Usually firewalld is the default on all CentOS 7 machines but you can switch to iptables as well
If using firewalld:
To open a TCP port using firewalld, you can use the following command,
firewall-cmd --zone=public --add-port=PORT_HERE/tcp --permanent
and for UDP ports you can use the below commands,
firewall-cmd --zone=public --add-port=12345/udp --permanent
Then, reload firewalld for the changes to take effect,
firewall-cmd --reload
If using iptables:
To open TCP/UDP port follow below command,
iptables -A INPUT -p tcp -m tcp --dport PORT_HERE -j ACCEPT
iptables -A INPUT -p udp -m udp --dport PORT_HERE -j ACCEPT
service iptables reload
Replace PORT_HERE with the port you wish to open.
Example
To open port 80,
IPTables
iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
iptables -A INPUT -p udp -m udp --dport 12345 -j ACCEPT
service iptables reload
Note: replace the Ports with actual ports
Firewalld
firewall-cmd --zone=public --add-port=80/tcp --permanent
firewall-cmd --reload
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