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Implementing Cisco Networking Solutions by Harpreet Singh

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Applying connection limits and TCP normalization

Hackers have another common method of attacking servers. This is called the SYN attack. In this attack, the attacker sends multiple TCP packets with the SYN flag on random source ports to the server to be attacked. The server sends a TCP packet in response to this connection request with the SYN and an ACK flag and waits for the returned ACK from the client, as TCP is a three-way handshake process. However, since the client was an attacker, the return ACK never comes and the server exhausts its resources waiting for the packets. This is called a SYN attack. If a number of hosts send TCP SYN packets to the attacked machine, unknowingly because a malware was installed on the attacking machines, ...

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