What is nftables?

What is nftables?

nftables is the modern Linux kernel packet classification framework. New code should use it instead of the legacy {ip,ip6,arp,eb}_tables (xtables) infrastructure. For existing codebases that have not yet converted, the legacy xtables infrastructure is still maintained as of 2021. Automated tools assist the xtables to nftables conversion process.

nftables in a nutshell:

• It is available in Linux kernels >= 3.13.

• It comes with a new command line utility nft whose syntax is different to iptables.

• It also comes with a compatibility layer that allows you to run iptables commands over the new nftables kernel framework.

• It provides a generic set infrastructure that allows you to construct maps and concatenations. You can use these new structures to arrange your ruleset in a multidimensional tree which drastically reduces the number of rules that need to be inspected until reaching the final action on a packet.

Why nftables?

We like iptables after all, this tool has been serving us (and will likely keep serving still for a while in many deployments) to filter out traffic on both per-packet and per-flow basis, log suspicious traffic activity, perform NAT and many other things. It comes with more than a hundred of extensions that have been contributed along the last 15 years!.

Nevertheless, the iptables framework suffers from limitations that cannot be easily worked around:

• Avoid code duplication and inconsistencies: Many of the iptables extensions are protocol specific, so there is no a consolidated way to match packet fields, instead we have one extension for each protocol that it supports. This bloats the codebase with very similar code to perform a similar task: payload matching.

• Faster packet classification through enhanced generic set and map infrastructure.

• Simplified dual stack IPv4/IPv6 administration, through the new inet family that allows you to register base chains that see both IPv4 and IPv6 traffic.

• Better dynamic ruleset updates support.

• Provide a Netlink API for third party applications, just as other Linux Networking and Netfilter subsystem do.

• Address syntax inconsistencies and provide nicer and more compact syntax.

These, among other things not listed here, triggered the nftables development which was originally presented to the Netfilter community in the 6th Netfilter Workshop in Paris (France).