Default Configuration of Firewalld Zones ZONE NAME The following table details these initial zone configuration. By default, all zones permit any incoming traffic which is part of a communication initiated by the system, and all outgoing traffic. (The trusted zone, which permits all traffic by default, is one exception to this.) Pre-defined Zonesįirewalld has pre-defined zones, each of which you can customize. If the traffic does not match a permitted port and protocol or service, it is generally rejected. Most zones allow traffic through the firewall, which matches a list of particular ports and protocols, such as 631/udp, or pre-defined services, such as ssh.
Initially, firewallddesignates the public zone as default, and maps the lo loopback interface to the trusted zone. The default zone is not a separate zone, but is a designation for an existing zone. If the network interface is not associated with a zone for some reason, then firewalld associates the packet with the default zone. If the source address is not assigned to a zone, firewalld associates the packet with the zone for the incoming network interface and the rules for that zone apply. If that source address is assigned to a specific zone, the rules for that zone apply. A user might want their system’s sshd service to be reachable when connected to their home and corporate networks, but not when connected to the public wireless network in the local coffee shop.įirewalld checks the source address for every packet coming into the system. This is especially useful when traveling between home, work, and public wireless networks. The zones are customized with rules appropriate for particular connections. Note: For laptops or other machines that regularly change networks, NetworkManager can be used to automatically set the firewall zone for a connection. Each zone has its own list of ports and services that are either open or closed. Based on criteria such as the source IP address of a packet or the incoming network interface, traffic is diverted into the firewall rules for the appropriate zone. With firewalld, firewall management is simplified by classifying all network traffic into zones. The firewalld subsystem, available from the firewalld RPM package, is not included in a minimal install, but is included in a base installation. Although strongly discouraged, firewalld can be configured to revert to the iptables back-end for complex use cases where existing iptables rulesets cannot be properly processed by nft translations.Īpplications query the subsystem using the D-Bus interface. Firewalld remains capable of reading and managing iptables configuration files and rulesets, using xtables-nft-multi to translate iptables objects directly into nftables rules and objects. In CentOS/RHEL 8, firewalld remains the recommended front end, managing firewall rulesets using nft. Until the introduction of nftables, firewalld used the iptables command to configure netfilter directly, as an improved alternative to the iptables service. Introducing firewalldįirewalld is a dynamic firewall manager, a front end to the nftables framework using the nft command.
Nftables uses the single nft user-space utility, allowing all protocol management to occur through a single interface, eliminating historical contention caused by diverse front ends and multiple netfilter interfaces. Netfilter is configured through multiple utility frameworks, including iptables, ip6tables, arptables, and ebtables, which are now deprecated.
Another major difference between nftables and the original netfilter are their interfaces.
The advantages of the nftables update is faster packet processing, faster ruleset updates, and simultaneous IPv4 and IPv6 processing from the same rules. The Linux kernel also includes nftables, a new filter and packet classification subsystem that has enhanced portions of netfilter’s code, but retaining the netfilter architecture such as networking stack hooks, connection tracking system, and the logging facility. Netfilter is the primary component in CentOS/RHEL 8 firewalls. Any incoming, outgoing, or forwarded network packet can be inspected, modified, dropped, or routed programmatically before reaching user space components or applications.
Firewall software uses these hooks to register filter rules and packet-modifying functions, allowing every packet going through the network stack to be processed. By implementing handlers in the kernel that intercept function calls and messages, netfilter allows other kernel modules to interface directly with the kernel’s networking stack. The Linux kernel includes netfilter, a framework for network traffic operations such as packet filtering, network address translation and port translation.