Random Musings

Can you explain this output:

[root@instance-20230204-0001 ~]# firewall-cmd --list-all
public (active)
target: default
icmp-block-inversion: no
interfaces: ens3
sources:
services: dhcpv6-client ssh
ports: 80/tcp
protocols:
forward: no
masquerade: no
forward-ports:
source-ports:
icmp-blocks:
rich rules:

This is the output of the firewall-cmd --list-all command, which provides details about the currently active firewall settings managed by firewalld. Here’s a line-by-line explanation of the output:

Output Breakdown:

1. public (active)
   • The zone is public, and it is currently active.
   • A zone in firewalld defines a specific set of rules applied to a network interface or source. The public zone is commonly used for untrusted networks, with limited access to services.
2. target: default
   • The target specifies the default action for packets that don’t match any rules in the zone. Here, default means it will apply the default behavior defined for the zone.
3. icmp-block-inversion: no
   • This indicates whether ICMP block inversion is enabled.
   • ICMP block inversion allows traffic by default and blocks only specified ICMP types. no means this feature is disabled.
4. interfaces: ens3
   • The network interface ens3 is bound to the public zone.
   • All traffic going through ens3 will follow the rules defined in the public zone.
5. sources:
   • No specific IP addresses or subnets are set as sources for this zone. If specified, traffic from those sources would follow the zone’s rules.
6. services: dhcpv6-client ssh
   • Allowed services in this zone are:
     • dhcpv6-client: Used for DHCPv6 communication (IPv6).
     • ssh: Allows Secure Shell (SSH) connections (usually on port 22).
7. ports: 80/tcp
   • The firewall is configured to allow incoming traffic on TCP port 80.
   • This port is commonly used for HTTP traffic (web servers).
8. protocols:
   • No specific protocols (e.g., TCP, UDP) are explicitly mentioned here, apart from the service and port definitions.
9. forward: no
   • Packet forwarding is disabled in this zone.
   • The firewall will not forward packets between different network interfaces.
10. masquerade: no
    • Network address translation (NAT) or masquerading is not enabled.
    • Masquerading is often used to allow multiple devices on a private network to share a single public IP address.
11. forward-ports:
    • No port forwarding rules are defined.
    • Port forwarding redirects traffic from one port to another, often on different systems.
12. source-ports:
    • No source-specific port rules are defined.
    • Source port rules control outgoing traffic based on the source port.
13. icmp-blocks:
    • No ICMP types (e.g., echo requests or pings) are blocked.
14. rich rules:
    • No rich rules are configured.
    • Rich rules provide advanced filtering options, such as time-based rules or matching specific packet characteristics.

Summary:

This firewall configuration allows the following:

• SSH (port 22) and DHCPv6-client services are permitted.
• HTTP traffic on port 80 (TCP) is allowed.
• Other traffic is denied by default (implicit in the public zone).
• No forwarding, masquerading, or additional custom rules are defined.

This configuration is suitable for a basic server setup requiring SSH and web access but not advanced routing or NAT functionalities.