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I have a lot of DDOS attacks lately and given only the attackers IP.

I want to block them via IPtables. Every time the range of IPs is the same but the actual IPs are different.

How can I create the proper range of IPs so I can block them via firewall while I do not know the netmask?

  • These days there are very clever attacks spread over entire ranges of IP addresses. What I do is: Lookup the source country for the IP, then lookup the overall subnet, then block that whole sub-net, as per Maythux's answer below. I do not care about collateral damage. More recently, I don't even bother looking up the country, I just go directly to the China or Hong Kong list. There are many sources, I use: freegeoip.net and ip2location.com/free/visitor-blocker – Doug Smythies Jun 17 '15 at 22:05
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Suppose the range of addresses is 192.168.1.*

To block is 192.168.1.* addresses:

sudo iptables -A INPUT -s is 192.168.1.0/24 -j DROP

To block is 192.168.. addresses:

sudo iptables -A INPUT -s 192.168.0.0/16 -j DROP

To block 192...* addresses:

sudo iptables -A INPUT -s 192.0.0.0/8 -j DROP

But you have to notice this will also block legitimate traffic from the same range

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  • thank you ! now i understand a bit better the concept of sub netting – Vitalik Jimbei Jun 17 '15 at 6:41
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You can also automate for unknown ip ranges, it by setting limits:

sudo iptables -A INPUT -m limit --limit 50/minute --limit-burst 200 -j ACCEPT
  • -m limit: This uses the limit iptables extension
  • –limit 50/minute: This limits only maximum of 50 connection per minute.
  • –limit-burst 200: This value indicates that the limit/minute will be enforced only after the total number of connection have reached the limit-burst level.

linux command to prevent dos attack by using netstat and iptables

http://blog.bodhizazen.com/linux/prevent-dos-with-iptables/

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  • could you please explain the rule for me please ? i'm new to all this and not sure i follow you. if i run a vpn protocol for my office won't this affect the connection for my colleagues ? – Vitalik Jimbei Jun 17 '15 at 8:26
  • edited: please double check the info. As far as i understand, only if more than 200 connections are established, the 50/min limit will get enforced. – aldwinaldwin Jun 17 '15 at 8:42
  • basically the rule says you can have 50 incoming connection per minute. all other will be dropped ? what does limit burst does then ? – Vitalik Jimbei Jun 17 '15 at 12:08
  • if you have more than 200 connections (limit-burst) then ... the ip's that try to connect more than 50 times per minute will be dropped – aldwinaldwin Jun 17 '15 at 12:11
  • i re-read your description again, now all clear. thank you , you've been very helpful ! – Vitalik Jimbei Jun 17 '15 at 12:22

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