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Firewall and Security Group

A Linux firewall is a network security tool that control and filter incoming and outgoing data packets, protecting the system from unauthorized access and network attacks.

Managing firewalls in Linux​

On Linux systems, use tools such as firewalld, iptables, and nftables to manage firewalls.

After installing firewalld, it exists as a daemon on the system.

Managing Security Group on cloud​

If there no firewall tool in your Linux system, you can enable Security Group on your cloud. Security groups on cloud and Firewalld in Linux both serve to control network traffic.

Major Cloud platform security group settings for your references:

FAQ​

How to test if a port is reachable?​

Use nc or telnet commands to test the port more efficiently than viewing the cloud console:

  • nc

    # Success result
    $ nc -zvw10 8.142.3.195 22
    Connection to 8.142.3.195 22 port [tcp/*] succeeded!

    # Failed result
    $ nc -zvw10 8.142.3.195 9091
    nc: connect to 8.142.3.195 port 9093 (tcp) failed: Connection refused

  • telnet

    # Success result
    $ telnet 8.142.3.195 22
    Trying 8.142.3.195...
    Connected to 8.142.3.195.
    Escape character is '^]'.

    # Failed result
    $ telnet 8.142.3.195 9091
    Trying 8.142.3.195...
    telnet: Unable to connect to remote host: Connection refused