this post was submitted on 22 Jul 2023
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They mean after adding a ddos mitigation like cloudflare, you should rotate the origin server IP so the origin server's IP is no longer publicly known and thus not directly reachable by ddos attackers. The only way to now interact with the application is though Cloudflare's network. You should only have to do this once as long as the origin IP doesn't publicly leak.
Another step would be to add firewall rules to only allow inbound traffic from cloudflare IPs: https://www.cloudflare.com/ips/
I recall a certain amount of overhead in IPTables "allow only from" situations but I'm not sure whether it's enough to make a DDOS any kind of viable on a server in this configuration.
Do you happen to know how effective the strategy is?
If your origin servers IP is never revealed then all traffic goes through cloudflare regardless. Firewall restricting the IPs is just good practice since cloudflare is the only IP that is supposed to talk to that server anyway, but it's not a requirement.
I can see some overhead if you're maintaining a large blacklist, but I don't see it happening with a small whitelist and default inbound DROP
Oh absolutely, I agree with the best practice! I just didn't know the real world efficacy of dropping packets near the NIC to mitigate DDOS load. There is certainly a performance limit but where that limit exists has been nebulous for me.