# Pare-feu

Voir `/critical/networking/nftables.md` pour une documentation minimale sur
NFTables.



Voici un pare-feu basique dans lequel des adhérants se trouvent derrière un
routeur :


```
#!/usr/sbin/nft -f

flush ruleset

#           +~~~~~~+
#           | IPV4 |
#           +~~~~~~+
define adh_prefix = 172.16.54.1 - 172.16.54.98
define srv_prefix = 185.230.79.0/24

define nat_out = 185.230.79.37

#           +~~~~~~+
#           | IPV6 |
#           +~~~~~~+
define adh_prefix6 = 2a0c:700:54::/64


# définit les adresses utilisées par les adhérants
define adh4 = 100.66.0.0/16 ### Qu'est-ce que cette adresse ?



#           +~~~~~~~~~~~~~~+
#           | Filter table |
#           +~~~~~~~~~~~~~~+
table inet filter {
	# Définiton des ports ouverts sur chaque machine
    # (Utilise un mapping plutôt que des sets pour éviter uen complexité
    #      terrifiante en O(nm) et passer à O(n+m) \(\ddot\smile\))
	set authorized_in_forward_tcp4 {
		type ipv4_addr . inet_service
		flags interval
	}
	set authorized_in_forward_udp4 {
		type ipv4_addr . inet_service
		flags interval
	}
	set authorized_in_forward_tcp6 {
		type ipv6_addr . inet_service
		flags interval
	}
	set authorized_in_forward_udp6 {
		type ipv6_addr . inet_service
		flags interval
	}

	chain input {
		type filter hook input priority 0; policy drop;

        # Accept local traffic
        meta iiftype loopback accept comment "allow from loopback"

		# Accepts existsing connections
		ct state { related, established } accept
		ct state invalid drop

        # Accept SSH and DHCP
        meta l4proto { udp, tcp } th dport { ssh, 67 } ct state new accept

		# Accept ping
		ip protocol icmp accept
		icmpv6 type { nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-router-advert, nd-neighbor-advert, echo-request, echo-reply } accept
	}

	chain forward {
		type filter hook forward priority 0; policy drop;

		# Accept established and ping connnections
		ct state { established, related } accept
		ct state invalid drop

        # On log tout ce qui est neuf et qui passe
        log prefix "FORWARD: "
		ip protocol icmp accept
		icmpv6 type { nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-router-advert, nd-neighbor-advert, echo-request, echo-reply } accept

		# Ouverture de ports pour les gens se trouvant derrière
		ip daddr . tcp dport @authorized_in_forward_tcp4 accept
		ip6 daddr . tcp dport @authorized_in_forward_udp4 accept
		ip daddr . udp dport @authorized_in_forward_tcp6 accept
		ip6 daddr . udp dport @authorized_in_forward_udp6 accept

		# Accepter toutes les connexions sortantes des clubs / adh et les logger
		ip saddr $adh_prefix accept
		ip6 saddr $adh_prefix6 accept
	}
}



#           +~~~~~+
#           | NAT |
#           +~~~~~+
table inet loggonsTout {
	chain prerouting {
		type nat hook prerouting priority dstnat;
		# On log ce qui est neuf
		ct state new log prefix "LOGALL: "
	}
}

table ip nat {
	chain postrouting {
		type nat hook postrouting priority srcnat;

		# traffic des adhérants et des clubs ===> $nat_out (range)
		ip saddr $adh_prefix snat to $nat_out persistent
	}
}
```