Firewall (iptables)

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Network Address Translation NAT

linux powerfull firewall

  • see the configuration running:
iptables -L
  • or

  • some rules:
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
ACCEPT     icmp --  anywhere             anywhere            icmp any
ACCEPT     ipv6-crypt--  anywhere             anywhere
ACCEPT     ipv6-auth--  anywhere             anywhere
ACCEPT     udp  --  anywhere            udp dpt:mdns
ACCEPT     udp  --  anywhere             anywhere            udp dpt:ipp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ipp
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere            state NEW tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere            state NEW tcp dpt:http
ACCEPT     tcp  --  anywhere             anywhere            state NEW tcp dpt:46590
ACCEPT     udp  --  anywhere             anywhere            state NEW udp dpt:46720
REJECT     all  --  anywhere             anywhere            reject-with icmp-host-prohibited

  • add a rule to accept connections on port 5901 (vncserver)
iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 5901 -j ACCEPT

saving configuration in a file

iptables-save > backup_iptables

restore conf from a file

iptables-restore < backup_iptables
  • this will only enable the configuration while iptables process is restarted, to avoid this, we need to save the configuration:
/etc/init.d/iptables save
  • now we can restart/reboot

redirecting connections

from a specified port to an host

iptables -A PREROUTING -d HOSTONE -p tcp -m tcp --dport 80 -j DNAT --to-destination HOSTWO:80
iptables -A POSTROUTING -d HOSTWO -j SNAT --to-source HOSTONE