In this article I gonna represent my home router config which also acting as a web/media/storage server and so on.

Warning I assume you got direct access to the host console, otherwise don't apply DROP policy until double-check the ACCEPT rules.

Here we do state that eth0 is connected to outer world and eth1 is our private network:

IF_INET=eth0
IF_PAN=eth1

Also define private network range:

NET_PAN=10.0.0.0/24

For fresh linux installation there should be no any rules, but let's clear them just in case:

iptables -F
iptables -t nat -F POSTROUTING

Now let's accept local traffic and ICMP packets to don't lose the host connection:

iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -i $IF_INET -p icmp --icmp-type 8 -j ACCEPT
iptables -A INPUT -i $IF_PAN -j ACCEPT

Also we would like to save already initiated connections:

iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

Now define NAT rules (and make sure that sysctl net.ipv4.ip_forward returns 1):

iptables -A POSTROUTING -t nat -j MASQUERADE
iptables -A FORWARD -i $IF_INET -o $IF_PAN -s $NET_PAN -j ACCEPT
iptables -A INPUT -i $IF_PAN -p icmp --icmp-type 8 -j ACCEPT

Then list all the services we would like to be reachable from outside:

# SSH (it's a good idea to change SSH port, by the way)
iptables -A INPUT -p tcp -i $IF_INET --dport 22 -j ACCEPT

# HTTP / HTTPS
iptables -A INPUT -i $IF_INET -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -i $IF_INET -p tcp --dport 443 -j ACCEPT

# SMTP
iptables -A INPUT -i $IF_INET -p tcp --dport 25 -j ACCEPT

# IGMP / IPTV
iptables -A FORWARD -p igmp -i $IF_INET -o $IF_PAN -j ACCEPT
iptables -A FORWARD -s 224.0.0.0/4 -j ACCEPT
iptables -A INPUT -s 224.0.0.0/4 -j ACCEPT

And the last step is to close the doors and deny all what is not allowed:

iptables -P INPUT DROP

Then I'd propose to install iptables-persistent and don't care about rules save and restore upon host reboot.


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