I am working on some iptables firewall rules and have seen many examples that suggest the importance of blocking potentially impossible traffic from non-routable IP address spaces. This would include items from RFC 1918, RFC 1700, RFC 5735, RFC 3927, RFC 3068, RFC 2544, RFC 5737, RFC 3171, and RFC 919. Some examples include the following:
Some of the examples indicate that you only need to worry about checking for this traffic if it is the source of the traffic. Example of:
$IPT -A ANTISPOOF -s 0.0.0.0/8 -m limit --limit 5/min --limit-burst 5 -j LOG --log-prefix "Denied Spoofed Source IP Address: " $IPT -A ANTISPOOF -s 0.0.0.0/8 -j DROP
In other examples, a more aggressive stance is taken where they check for the source and destination for both input and output. Examples include:
iptables -A INPUT -d 18.104.22.168/8 -j DROP iptables -A INPUT -s 22.214.171.124/8 -j DROP iptables -A OUTPUT -d 126.96.36.199/8 -j DROP iptables -A OUTPUT -s 188.8.131.52/8 -j DROP
I remain with the following questions:
- Do I need to check for the source address of the IP ranges listed above in the bulleted list?
- Do I need to check for the destination address of the IP ranges listed above in the bulleted list?
- Is is important to create rules for the IP ranges listed above that would include both the INPUT and OUTPUT chains?
- Are there any IP ranges that I have forgotten to check from that are missing from the bulleted list above?
Thanks in advance for your help with this.