#!/usr/sbin/nft -f
#
# This configuration file is customized by fox,
# Optimize nftables rules for local TS server.
#

table inet router
flush table inet router

table inet router {

    #
    # Flowtable
    #

    flowtable ft {
        hook ingress priority filter;
        devices = { eth0 };
        counter;
    }


    #
    # Filter rules
    #

    chain input {
        type filter hook input priority filter; policy drop;
        iif "lo" accept comment "defconf: accept traffic from loopback"
        ct state established,related accept comment "defconf: handle inbound flows"
        tcp flags & (fin | syn | rst | ack) == syn jump syn_flood comment "defconf: rate limit new TCP connections"
        iifname "eth0" accept comment "defconf: accept LAN IPv4 / IPv6 input traffic"
        iifname "tailscale0" goto accept_from_tailscale comment "tsconf: handle TS IPv4 / IPv6 input traffic"
    }

    chain forward {
        type filter hook forward priority filter; policy drop;
        ct state established,related flow add @ft accept comment "defconf: offload and accept forwarded flows"
        iifname "eth0" goto forward_lan comment "defconf: handle LAN IPv4 / IPv6 forward traffic"
        iifname "tailscale0" goto forward_tailscale comment "tsconf: handle TS IPv4 / IPv6 forward traffic"
    }

    chain output {
        type filter hook output priority filter; policy accept;
        oif "lo" accept comment "defconf: accept traffic towards loopback"
        ct state established,related accept comment "defconf: handle outbound flows"
        oifname "eth0" goto accept_to_lan comment "defconf: handle LAN IPv4 / IPv6 output traffic"
        oifname "tailscale0" goto accept_to_tailscale comment "tsconf: handle TS IPv4 / IPv6 output traffic"
    }

    chain syn_flood {
        limit rate 50/second burst 100 packets return comment "defconf: accept new TCP connections below rate-limit"
        counter drop comment "defconf: drop excess new TCP connections"
    }

    chain forward_lan {
        oifname "tailscale0" goto accept_to_tailscale comment "tsconf: accept LAN to TS forwarding"
        ct status dnat accept comment "lanconf: accept port forwards"
        oifname "eth0" goto accept_to_lan
    }

    chain forward_tailscale {
        oifname "eth0" goto accept_to_lan comment "tsconf: accept TS to LAN forwarding"
        oifname "tailscale0" goto accept_to_tailscale
    }

    chain accept_to_lan {
        meta nfproto ipv4 ct state invalid counter drop comment "defconf: prevent LAN NATv4 leakage"
        accept comment "defconf: accept LAN IPv4 / IPv6 traffic"
    }

    chain accept_from_tailscale {
        meta nfproto ipv4 counter accept comment "tsconf: accept TS IPv4 traffic"
        meta nfproto ipv6 counter accept comment "tsconf: accept TS IPv6 traffic"
    }

    chain accept_to_tailscale {
        meta nfproto ipv4 counter accept comment "tsconf: accept TS IPv4 traffic"
        meta nfproto ipv6 counter accept comment "tsconf: accept TS IPv6 traffic"
    }


    #
    # NAT rules
    #

    chain dstnat {
        type nat hook prerouting priority dstnat; policy accept;
        iifname { "eth0", "tailscale0" } meta l4proto { tcp, udp } th dport domain goto redirect_dns comment "defconf: handle LAN IPv4 / IPv6 dstnat traffic"
    }

    chain srcnat {
        type nat hook postrouting priority srcnat; policy accept;
        oifname "eth0" meta nfproto ipv4 counter masquerade comment "defconf: masquerade LAN IPv4 traffic"
    }

    chain redirect_dns {
        meta nfproto ipv4 counter redirect comment "lanconf: LAN IPv4 DNS redirect"
        meta nfproto ipv6 counter redirect comment "lanconf: LAN IPv6 DNS redirect"
    }


    #
    # Mangle rules
    #

    chain mangle_postrouting {
        type filter hook postrouting priority mangle; policy accept;
        oifname "eth0" tcp flags & (fin | syn | rst) == syn tcp option maxseg size set rt mtu comment "defconf: zone LAN IPv4 / IPv6 egress MTU fixing"
    }

    chain mangle_forward {
        type filter hook forward priority mangle; policy accept;
        iifname "eth0" tcp flags & (fin | syn | rst) == syn tcp option maxseg size set rt mtu comment "defconf: zone LAN IPv4 / IPv6 ingress MTU fixing"
    }

}