“Lock the self-replacement of SIM” at Kyivstar

Usually, simple SIM cards of the Kyivstar mobile operator, bought in some kind of stall or store, can be replaced independently with a new SIM card, for example, you can buy another SIM card there and call the operator, say that the old card is lost, report the last few dialed and accepted numbers, then the operator will block the old SIM card and activate a new one but with the same number that was on the old one.

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How to remove an IP address from email blacklists

Once I had to remove from the blacklists IP addresses of different dedicated servers located in data centers, since some mail services did not receive emails from them, due to the fact that the previous tenant did not use the IP address honestly or had viruses, spammed, and the current one got locks.

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The script against DDOS attacks

I will give an example of a simple script against DDOS attacks for NAT servers.
The script is executed when the total number of “conntrack” connections is more than 500000, it saves to the text file the IP address which has the most “conntrack” connections, who has more than 10,000 – adds to the ipset list.

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