Iptables

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iptables command line utility allows to modify Linux kernel firewall rules.


Basic commands

  • sudo iptables -L
  • iptables-save and iptables-restore
  • apt-get install iptables-persistent


  • Add: iptables -A
  • Delete: iptables -D

Examples

KVM VNC remote viewer
iptables -t nat -A PREROUTING -i eno1 -p tcp --dport 5900 -j DNAT --to 127.0.0.1:5900
sysctl -w net.ipv4.ip_forward=1
sysctl -p /etc/sysctl.conf


  • Block all output traffic: iptables -A OUTPUT -o ethXXX -j DROP


Open a port

 iptables -I INPUT -p tcp --dport XXX -j ACCEPT


Block all but a range

iptables -I OUTPUT -m iprange --dst-range <remote_ip>  -j ACCEPT
iptables -I INPUT -m iprange --src-range <remote_ip> -j ACCEPT
iptables -P INPUT DROP
iptables -P OUTPUT DROP
netfilter-persistent save


Block all but one IP

iptables -I OUTPUT -d <remote_ip>  -j ACCEPT
iptables -I INPUT -s <remote_ip> -j ACCEPT
iptables -I OUTPUT -d <remote_ip> -j ACCEPT
iptables -I INPUT -s <remote_ip> -j ACCEPT
iptables -P INPUT DROP
iptables -P OUTPUT DROP


Allow ssh connections only from specific IPs:

iptables -A INPUT -p tcp --dport 22 -s YourIP -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j DROP
netfilter-persistent save

Activities

  1. Read iptables Ubuntu howto: https://help.ubuntu.com/community/IptablesHowTo
  2. Read archlinux documentation: https://wiki.archlinux.org/index.php/iptables
  3. Read Stackoverflow iptables questions: https://stackoverflow.com/questions/tagged/iptables?tab=Votes
  4. Review your current iptables configuration
  5. iptables-save

See also

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