A SYN | ACK flagged bit sent to a closed port elicits a RST response, while an open port will not reply. This is because the TCP protocol requires a SYN flag to initiate the connection.
This scan has a tendency to register fairly large false positives. For instance , packets dropped by filtering devices, network traffic, timeouts etc can given a wrong inference of an open port while the port may or may not be open.
The server ignores the SYN | ACK packet sent to an OPEN PORT.
This scan has a tendency to register fairly large false positives. For instance , packets dropped by filtering devices, network traffic, timeouts etc can given a wrong inference of an open port while the port may or may not be open.
The server ignores the SYN | ACK packet sent to an OPEN PORT.
client -> SYN | ACK
server -> -
server -> -
Advantages : fast, avoids basic IDS/firewalls, avoids TCP three-way handshake
Disadvantages: less reliable (false positives)
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