Contents
Can iptables prevent DDoS?
While one can do a lot with iptables to block DDoS attacks, there isn’t a way around actual hardware firewalls (we recently reviewed RioRey DDoS mitigation hardware) to detect and stop large DDoS floods. However, it isn’t impossible to filter most bad traffic at line rate using iptables!
What is Synproxy?
SYNPROXY is a TCP SYN packets proxy. It can be used to protect any TCP server (like a web server) from SYN floods and similar DDos attacks. SYNPROXY is a netfilter module, in the Linux kernel. The valid TCP connections will pass through and served, while the attack will be stopped at the firewall.
What does a SYN cookie do?
SYN cookies is a technical attack mitigation technique whereby the server replies to TCP SYN requests with crafted SYN-ACKs, without inserting a new record to its SYN Queue. Only when the client replies this crafted response a new record is added.
How to use iptables to stop common DDoS attacks?
The above rule will tell IPtables to drop (refuse) flag-less packets This type of attack is when a malicious user can connect to your server without sending or receiving any information. The main reason a user would do this is to consume the resources on your server. You can use the rule below to block SYN-Flood attacks
How to increase the performance of iptables rules?
The best solution to dramatically increase the performance of your iptables rules and therefore the amount of (TCP) DDoS attack traffic they can filter is to use the mangle table and the PREROUTING chain! Another common mistake is that people don’t use optimized kernel settings to better mitigate the effects of DDoS attacks.
Is it possible to filter bad traffic using iptables?
However, it isn’t impossible to filter most bad traffic at line rate using iptables! We’ll only cover protection from TCP-based attacks. Most UDP-based attacks are amplified reflection attacks that will exhaust the network interface card of any common server.
Can a SYN flood attack slip through iptables?
While the iptables rules that we provided above already block most TCP-based attacks, the attack type that can still slip through them if sophisticated enough is a SYN flood.