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Firewall (nftables) · pro · solved in-browser (no VM needed) · 3 tiered hints

Write /etc/nftables.conf with a table ip mangle and a prerouting chain (type filter hook prerouting priority mangle). Divert outbound web traffic to a local proxy: for `tcp dport 80`, redirect it with `tproxy to :3129` and set a packet mark of 1 with `meta mark set 1`. (Authored config, graded structurally — the engine isn't run here.)

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