Firewall (iptables)

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NAT

Network Address Translation NAT

linux powerful firewall

  • print out the configuration running:
iptables -L
  • or better (this will print all tables and chains)
iptables-save

  • 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             224.0.0.251         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

UFW

The Ubuntu Firewall

ufw deny from 10.0.0.42
ufw deny in on eth0 from 10.0.0.42
ufw allow ssh
ufw allow 22
ufw allow from 10.0.0.0/24  to any port 22
ufw allow from 10.0.0.0/24 to any port 873
ufw allow http
ufw allow 80
ufw allow https
ufw allow 443
ufw allow proto tcp from any to any port 80,443

Allow MySQL from Specific IP Address or Subnet

ufw allow from 10.0.0.0/24 to any port 3306

Allow MySQL to Specific Network Interface

ufw allow in on eth1 to any port 3306

PostgreSQL from Specific IP Address or Subnet

ufw allow from 10.0.0.0/24 to any port 5432