Centos 7 - How to firewalld

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Firewalld and Centos 7

'A quick guide, how to use firewalld with Centos 7.'

To use firewalld, start it:

      systemctl start firewalld 
      systemctl enable firewalld 
       

By default, "public" zone is applied with a NIC and dhcpv6-client and ssh are allowed. When operating with "firewall-cmd" command, if you input the command without "--zone=***" specification, then, configuration is set to the default zone.

    • drop: Any incoming network packets are dropped, there is no reply. Only outgoing network connections are possible.
    • block: Any incoming network connections are rejected with an icmp-host-prohibited message for IPv4 and icmp6-adm-prohibited for IPv6. Only network connections initiated from within the system are possible.
    • public: For use in public areas. You do not trust the other computers on the network to not harm your computer. Only selected incoming connections are accepted.
    • external: For use on external networks with masquerading enabled especially for routers. You do not trust the other computers on the network to not harm your computer. Only selected incoming connections are accepted.
    • dmz: For computers in your demilitarized zone that are publicly-accessible with limited access to your internal network. Only selected incoming connections are accepted.
    • work: For use in work areas. You mostly trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.
    • home: For use in home areas. You mostly trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.
    • internal: For use on internal networks. You mostly trust the other computers on the networks to not harm your computer. Only selected incoming connections are accepted.
    • trusted: All network connections are accepted.

Change to default zone (public) firewall-cmd --get-default-zone

Display current settings firewall-cmd --list-all

Display all zones defined by default firewall-cmd --list-all-zones

Display allowed services on a specific zone firewall-cmd --list-service --zone=external

Change default zone firewall-cmd --set-default-zone=external

Change zone for an interface (not changed permanently) firewall-cmd --change-interface=eth1 --zone=external

If need to change it permanently, use nmcli like follows nmcli c mod eth1 connection.zone external

Display services defined by default

      firewall-cmd --get-services
      # definition files are placed like follows
      # if you'd like to add your original definition, add XML file on there
      ls /usr/lib/firewalld/services 

Add or remove allowed services

The change will be back after rebooting the system. If you change settings permanently, add the "--permanent" option.

       # for example, add http (the change will be valid at once)      
       firewall-cmd --add-service=http 
       firewall-cmd --list-service 
       # for example, remove http
       firewall-cmd --remove-service=http
       firewall-cmd --list-service
       # for example, add http permanently
       firewall-cmd --add-service=http --permanent 
       firewall-cmd --reload 
       firewall-cmd --list-service 
        

Add or remove allowed ports

       # for example, add TCP 465      
       firewall-cmd --add-port=465/tcp 
       firewall-cmd --list-port 

       # for example, remove TCP 465
       firewall-cmd --remove-port=465/tcp 
       firewall-cmd --list-port
       # for example, add TCP 465 permanently
       firewall-cmd --add-port=465/tcp --permanent 
       firewall-cmd --reload
       firewall-cmd --list-port 

Add or remove prohibited ICMP types

       # for example, add echo-request to prohibit it
       firewall-cmd --add-icmp-block=echo-request 
       firewall-cmd --list-icmp-blocks
       # for example, remove echo-request
       firewall-cmd --remove-icmp-block=echo-request 
       firewall-cmd --list-icmp-blocks
       # display ICMP types
       firewall-cmd --get-icmptypes          
        

Online resources

Red Hat

Server World