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litespeed_wiki:config:mitigating-ddos-attacks [2019/05/14 20:26] Jackson Zhang [Check concurrent connections] |
litespeed_wiki:config:mitigating-ddos-attacks [2019/05/15 19:25] Lisa Clarke [Analysis of IPs from attacked] Copyediting |
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| Please keep in mind that ''netstat -ntu'' will list TCP in TIME_WAIT state, which will inflate the number. For the correct concurrent TCP connections counting method, you should only count TCPs in ''ESTABLISHED'' state. Hence ''grep ESTA'' or ''grep ESTABLISHED'' will be required. | Please keep in mind that ''netstat -ntu'' will list TCP in TIME_WAIT state, which will inflate the number. For the correct concurrent TCP connections counting method, you should only count TCPs in ''ESTABLISHED'' state. Hence ''grep ESTA'' or ''grep ESTABLISHED'' will be required. | ||
| - | ==== Analysis of IPs from attacked ==== | + | ==== Analysis of IPs from Attacker ==== |
| - | If you don't necessarily count concurrent connections, just want to analyze which IPs might be attacker, you can check time_waits connection as well. You can run the command without ''grep ESTABLISHED'': | + | |
| - | netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -nr | + | |
| - | An attacker could make a connection, send requests to expensive URL, wait a little while, then close connection, if server does not abort the process, the backend will be used up soon and keep serving request that has been abandoned. The above command will be useful during the situation. | + | Bad IP's can make quick connections, and you end up with many ''time_waits'' which you won't see when just looking at established. |
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| + | If you don't necessarily count concurrent connections, and just want to analyze which IPs might be attackers, you can include ''time_waits'' connections. Run the command without ''grep ESTABLISHED'', which gives you the ability to see what IP's just connected and dropped and may need to be blocked: | ||
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| + | netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n | awk '$1 >= 5 {print $0}' | ||
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| + | An attacker could make a connection, send requests to an expensive URL, wait a little while, and then close the connection. If the server does not abort the process, the backend will be used up soon, as it will keep serving requests that have been abandoned. The above command will be useful during such a situation. | ||
| ==== Check the Banned IP and Reason ==== | ==== Check the Banned IP and Reason ==== | ||
| If an IP has been banned, but you don't know why, you can check it with SSH. Here is an example of a connection that was banned because it reached the hard limit. | If an IP has been banned, but you don't know why, you can check it with SSH. Here is an example of a connection that was banned because it reached the hard limit. | ||