Default firewall configuration using iptables for a fresh Ubuntu 14.04 server.

iptables.sh

#!/bin/sh -x

# ================================== 
# iptables default configuration script
#
# - this locks down our servers port access
# ==================================

# install fail2ban
sudo apt-get update
sudo apt-get install fail2ban -y

#reset the default input / output policies and flush any existing rules
sudo iptables -P INPUT ACCEPT
sudo iptables -P OUTPUT ACCEPT
sudo iptables -F

# Accept incoming packets from established or existing connections
sudo iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT

# enable SSH and web ports
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT

# enable loopback (localhost) access
sudo iptables -I INPUT 1 -i lo -j ACCEPT

# add any reuquired subnet restrictions
# sudo iptables -A INPUT -s 10.0.0.0/24 -j ACCEPT

# set the last rule to drop all traffic, this is better than
# changing the defualt policy as this can lock you out
sudo iptables -A INPUT -j DROP

# clone the config file (its updated with package updates), so we need a clone
sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local

# Note:
# - if running nginx, then edit the file and enable the jail for it
# - we might also want to extend the bantime to something like 1800
# sudo nano /etc/fail2ban/jail.local

# restart the service
sudo service fail2ban stop
sudo service fail2ban start

# persist the changes across restarts
sudo apt-get install iptables-persistent

# save for restarts
iptables-save > /etc/iptables/rules.v4
ip6tables-save > /etc/iptables/rules.v6

# check the policy
# sudo iptables -S

Inspiration:

https://www.digitalocean.com/community/articles/how-to-set-up-a-firewall-using-iptables-on-ubuntu-14-04
https://www.digitalocean.com/community/articles/how-to-install-and-use-fail2ban-on-ubuntu-14-04

To add an IP restriction, use the following:

# list with line numbers
sudo iptables -L --line-numbers

# remove last rule (drop all)
iptables -D INPUT <line>

# add ip restriction
sudo iptables -A INPUT -s xx.xx.xx.xx -j ACCEPT
sudo iptables -A INPUT -j DROP

# save changes
iptables-save > /etc/iptables/rules.v4
ip6tables-save > /etc/iptables/rules.v6

# verify changes
sudo iptables -S