Nftables

command line syntax

A command to drop any packets with the destination IP address 1.2.3.4

nft add rule ip filter output ip daddr 1.2.3.4 drop

The syntax of iptables is different:

iptables -A OUTPUT -d 1.2.3.4 -j DROP

Also, there is a planned compatibility layer for the translation of already existing iptables firewall rules into their nftables equivalents.

History

The project was first publicly presented at Netfilter Workshop 2008 by Patrick McHardy from the Netfilter Core Team. The first preview release of kernel and userspace implementation was given in March 2009. Although the tool has been called, "...the biggest change to Linux firewalling since the introduction of iptables in 2001", it has received little press. Notable hacker Fyodor Vaskovich (Gordon Lyon) said that he is "looking forward to its general release in the mainstream Linux kernel."

The project stayed in alpha stage and the official website was removed in 2009. In March 2010, emails from the author on the project mailing lists showed the project was still active and approaching a beta release, but the latter was never shipped officially. In October 2012, Pablo Neira Ayuso proposed a compatibility layer for iptables and announced a possible inclusion of the project into mainstream kernel.

On 16 October 2013, Pablo Neira Ayuso submitted a nftables core pull request to the Linux kernel mainline tree. It was merged into the kernel mainline on 19 January 2014, with the release of Linux kernel version 3.13.

Overview

The nftables kernel engine adds a simple virtual machine into the Linux kernel which is able to execute bytecode to inspect a network packet and make decisions on how that packet should be handled. The operations implemented by this virtual machine are intentionally made basic. It can get data from the packet itself, have a look at the associated metadata (inbound interface, for example), and manage connection tracking data. Arithmetic, bitwise and comparison operators can be used for making decisions based on that data. The virtual machine is also capable of manipulating sets of data (typically IP addresses), allowing multiple comparison operations to be replaced with a single set lookup.

The above-described organization is contrary to the iptables firewalling code, which has protocol awareness built-in so deeply into the logic that the code has had to be replicated four times—for IPv4, IPv6, ARP, and Ethernet bridging—as the firewall engines are too protocol-specific to be used in a generic manner.

The main advantages of nftables over iptables are the simplification of the Linux kernel ABI, reduction of code duplication, improved error reporting, and more efficient execution, storage and incremental changes of filtering rules. Traditionally used iptables(8), ip6tables(8), arptables(8) and ebtables(8) (for IPv4, IPv6, ARP and Ethernet bridging, respectively) are intended to be replaced with nft(8) as a single unified implementation, providing firewall configuration on top of the in-kernel virtual machine.

nftables also offers an improved userspace API that allows atomic replacements of one or more firewall rules within a single Netlink transaction. That speeds up firewall configuration changes for setups having large rulesets; it can also help in avoiding race conditions while the rule changes are being executed. Also, a planned compatibility layer is going to provide translation of already existing iptables firewall rules into their nftables equivalents.