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open notes/homework/labs / no googling ;)
port scanning is for the good guys for pen-testing to check for vulnerabilities on the network but the bad guys can use it too.
3 way handshake is completed to save resources
do enough 2 way handshakes to kill a server?
once a 3 way handshake is made the server has logged you in so you are known
SYN scan - nmap scanner ------------------ target
open port : sends a SYN packet and a SYN ACK back and the scanner sends back a RST (reset) because they want to end the handshake to not leave them hanging and save memory
closed port : sends SYN and a RST is sent back
* not used to detect firewall *
Connect scan - nmap scanner -------------------------- target
never start with a connect scan, use it only if you dont have admin access on your system
open port : full 3 way handshake SYN / SYN ACK / ACK followed by a RST
closed port : sends SYN and an RST is sent back
FIN scan - nmap scanner ------------------------------ target
cannot tell you if there is a firewall
FIN packet closes the communication
W open port : sends FIN packet and RST is sent back
L open port : sends FIN packet (closes communication) and nothing is sent back
closed port : sends FIN and RST is sent back for both W and L
FIN/XMAS/Null
ACK scan - nmap scanner ----------------------- target
open port : sends ACK and a RST is sent back always
filtered port / firewall : sends ACK and and it is dropped, nothing is sent back
RFC793 TCP standard (Request For Common)
- this says that if you get a unknown packet you send nothing back but microsoft decided to do things different, if you get an unknown packet they always respond with an RST
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