How do I deny all requests not from cloudflare?

Posted by phillips1012 on Server Fault See other posts from Server Fault or by phillips1012
Published on 2014-06-03T01:38:42Z Indexed on 2014/06/03 3:30 UTC
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nginx

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cloudflare

I've recently gotten denial of service attacks from multiple proxy ips, so I installed cloudflare to prevent this. Then I started noticing that they're bypassing cloudflare by connecting directly to the server's ip address and forging the host header.

What is the most performant way to return 403 on connections that aren't from the 18 ip addresses used by cloudflare?
I tried denying all then explicitly allowing the cloudflare ips but this doesn't work since I've set it up so that CF-Connecting-IP sets the ip allow tests for.

I'm using nginx 1.6.0.

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