Linux/iptables

Tables Chains FILTER INPUT FORWARD OUTPUT NAT PREROUTING OUTPUT POSTROUTING MANGLE (modify ip headers) PREROUTING INPUT FORWARD OUTPUT POSTROUTING RAW (connection tracking) PREROUTING OUTPUT (SECURITY) (SELinux) INPUT FORWARD OUTPUT		Targets valid in note REJECT INPUT, FORWARD, OUTPUT sends response back DROP no response ACCEPT RETURN MASQUERADE POSTROUTING REDIRECT NAT:PREROUTING + NAT:OUTPUT

Basics

iptables
         -A (append - add rule at end)             -i (input interface)          -j (target)
         -C (check)                                -o (output interface)
         -D (delete - remove rule)                 -s (source address)    
         -F (flush - remove all rules)             -d (destination address)
         -I (insert - add at position)              
         -L (list - show all rules in chain)       -p      (protocol (tcp/udp))
         -N (new chain)                            --dport (destination port)
         -X (delete chain)                         --sport (source port)

         -t (table to manipulate (default: filter)

         -n (numeric output of addresses and ports)

View state

iptables-save                  # show everything

iptables --list-rules          # list filter rules (default: filter)
iptables --list-rules -t nat   # list nat rules

Random examples

iptables -A INPUT -p tcp --dport 22 -j ACCEPT

• openvpn

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
iptables -t nat -A POSTROUTING -o tun0 -j MASQUERADE

• wireguard

iptables -A FORWARD -i wg0 -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

iptables -D FORWARD -i wg0 -j ACCEPT
iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE

• raspi wifi to ethernet

iptables --table nat --append POSTROUTING --out-interface wlan0 -j MASQUERADE
iptables --append FORWARD --in-interface eth0 -j ACCEPT

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT

Links

• https://www.frozentux.net/iptables-tutorial/iptables-tutorial.html
• https://gist.github.com/mcastelino/c38e71eb0809d1427a6650d843c42ac2
• http://rudijs.github.io/2015-07/docker-restricting-container-access-with-iptables/