Nftables
Patrick McHardy intended to replace iptables with (the now defunct) nftables in the future. The four modules of iptables (IPv4, IPv6, ARP, and Ethernet bridging) are replaced with a single unified implementation, implemented on the top of a virtual machine.
The project was in the alpha stage of development when it went dormant (in 2009). There since has been no word as to what the future of nftables is.
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