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I would like to allow only HTTP(S) traffic coming from CloudFlare. In that way attackers cannot attack the server directly. I know CloudFlare is not mainly a DDoS mitigator, but I would like to try it either way.

I'm currently only having access to iptables (ipv4 only), but will try to install ip6tables soon. I just need to have this fixed soon. (we're getting (D)DoSed atm.)

I was thinking about something like this:

iptables -I INPUT -s <CloudFlare IP> --dport 80 -j ACCEPT
iptables -I INPUT -s <CloudFlare IP> --dport 443 -j ACCEPT
iptables -I INPUT -p tcp --dport 80 -j DROP
iptables -I INPUT -p tcp --dport 443 -j DROP

I know that CloudFlare has multiple IPs, but just for an example.

Would this be the right way?

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up vote 5 down vote accepted

Yes, that would work. You can also use ! to negate like this:

iptables -I INPUT ! -s <cloud_flare ip> -p tcp --dport 80 -j DROP
iptables -I INPUT ! -s <cloud_flare ip> -p tcp --dport 443 -j DROP
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Ah great, I didn't know about that. Is it also possible to use that with multiple IPs? I need to accept about 10 IP ranges from CloudFlare. – Martin Nov 7 '12 at 10:30
From the manpage: Multiple addresses can be specified, but this will expand to multiple rules (when adding with -A), or will cause multiple rules to be deleted (with -D). – miono Nov 7 '12 at 10:31
so like: iptables -I INPUT ! -s <cloud_flare ip1> -p tcp --dport 80 -j DROP iptables -I INPUT ! -s <cloud_flare ip2> -p tcp --dport 80 -j DROP? – Martin Nov 7 '12 at 10:33
Ah sweet. Thanks a bunch, I will try it soon – Martin Nov 7 '12 at 10:36
Sorry, obviously it's not possible to give many addresses when used with !, you'll have to create multiple rules. – miono Nov 7 '12 at 10:38

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