#!/usr/bin/nft -f flush ruleset table inet filter { chain prerouting-raw { type filter hook prerouting priority raw # drop packets without a reverse path (strict reverse path filtering) fib saddr . iif oif missing counter drop iif lo notrack accept # drop packets to address not configured on incoming interface (strong host model) fib daddr . iif type != { local, broadcast, multicast } counter drop # reject SSH packets via anycast IP tcp dport 22 ip daddr 198.251.90.93 reject with tcp reset udp dport 53 notrack accept tcp dport {22, 53, 80, 443, 853} notrack accept meta l4proto {icmp, ipv6-icmp} notrack accept } chain output-raw { type filter hook output priority raw oif lo notrack accept udp sport 53 notrack accept tcp sport {22, 53, 80, 443, 853} notrack accept meta l4proto {icmp, ipv6-icmp} notrack accept } chain input { type filter hook input priority filter policy drop iif lo accept udp dport 53 accept tcp dport {22, 53, 80, 443, 853} accept meta l4proto {icmp, ipv6-icmp} accept ct state vmap { invalid : drop, established : accept, related : accept } meta l4proto udp reject meta l4proto tcp reject with tcp reset reject } chain forward { type filter hook forward priority filter policy drop } chain output { type filter hook output priority filter oif lo goto output-internal skuid != {root, systemd-network, unbound, chrony, http, powerdns, geoipupdate} counter goto output-reject } chain output-internal { skuid unbound meta l4proto {tcp, udp} th sport 53 th dport >= 1024 accept skuid {chrony, geoipupdate} meta l4proto {tcp, udp} th sport >= 1024 th dport 53 accept skuid powerdns meta l4proto tcp th sport 54 th dport >= 1024 accept skuid http meta l4proto {tcp, udp} th sport >= 1024 th dport 54 accept skuid powerdns meta l4proto tcp th sport 81 th dport >= 1024 accept skuid != root counter goto output-reject accept } chain output-reject { meta l4proto udp reject meta l4proto tcp reject with tcp reset reject } }