Linux command: iptables

List current rules

iptables -l List firewall rules

Collection of basic Linux Firewall iptables rules

Reject all outgoing network connections

iptables -F OUTPUT
iptables -A OUTPUT -m state --state ESTABLISHED -j ACCEPT
iptables -A OUTPUT -j REJECT

iptables to reject all incoming network connections

iptables -F INPUT
iptables -A INPUT -m state --state ESTABLISHED -j ACCEPT
iptables -A INPUT -j REJECT

iptables to reject all network connections

iptables -F
iptables -A INPUT -j REJECT
iptables -A OUTPUT -j REJECT
iptables -A FORWARD -j REJECT

iptables to drop incoming ping requests

iptables -A INPUT -p icmp --icmp-type echo-request -j DROP

iptables to drop outgoing telnet connections

iptables -A OUTPUT -p tcp --dport telnet -j REJECT

iptables to reject incoming telnet connections

iptables -A INPUT -p tcp --dport telnet -j REJECT

iptables to reject outgoing ssh connections

iptables -A OUTPUT -p tcp --dport ssh -j REJECT

iptables to reject incoming ssh connections

iptables -A INPUT -p tcp --dport ssh -j REJECT

iptables to reject all incoming traffic except ssh and local connections

iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -p tcp --dport ssh -j ACCEPT
iptables -A INPUT -j REJECT

iptables to accept incoming ssh connections from specific IP address

iptables -A INPUT -p tcp -s 77.66.55.44 --dport ssh -j ACCEPT
iptables -A INPUT -p tcp --dport ssh -j REJECT

iptables to accept incoming ssh connections from specific MAC address

iptables -A INPUT -m mac --mac-source 00:e0:4c:f1:41:6b -p tcp --dport ssh -j ACCEPT
iptables -A INPUT -p tcp --dport ssh -j REJECT

iptables to reject incoming connections on a specific TCP port

iptables -A INPUT -p tcp --dport 3333 -j REJECT

iptables to drop all incoming connections on a specific network interface

iptables -A INPUT -i eth0 -s 192.168.0.0/16 -j DROP

iptables to create a simple IP Masquerading

The following rule will create a simple IP Masquerading gateway to allow all host on the same subnet to access the Internet.
The below specified eth0 is a external interface connected to the Internet.

echo "1" > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o $EXT_IFACE -j MASQUERADE

Reject all incoming telnet traffic except specified IP address

iptables -A INPUT -t filter ! -s 222.111.111.222 -p tcp --dport 23 -j REJECT

Reject all incoming ssh traffic except specified IP address range

iptables -A INPUT -t filter -m iprange ! --src-range 10.1.1.90-10.1.1.100  -p tcp --dport 22 -j REJECT

Removing negator "!" from the below rule reject all ssh traffic originating from IP address range 10.1.1.90 - 10.1.1.100.

iptables to reject all outgoing traffic to a specific remote host

iptables -A OUTPUT -d 222.111.111.222 -j REJECT

iptables to block an access to a specific website

iptables -A INPUT -s facebook.com -p tcp --sport www -j DROP