April 2005
Intermediate to advanced
344 pages
11h 59m
English
Content preview from Network Security Tools
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Overview of SYNplescan
Half-open
(or SYN scanning)
works by taking advantage of the
three-way handshaking process the TCP protocol uses to establish a
connection. The three-way handshaking process, as shown in Figure 11-3, involves the system initiating the connection
to send a TCP packet with the SYN flag set. If the
port the system is attempting to connect to is accepting connections,
the destination system responds with a TCP packet with the
SYN and ACK flags set. To
complete the connection, the initiating system sends a TCP packet
back with the ACK flag set.
Figure 11-3. TCP three-way handshake
This is in contrast to the situation shown in Figure 11-4, in which the initiating system is attempting
to connect to a TCP port that is closed. In this case the destination
host responds with a TCP packet with the SYN and
RST flags set.
Figure 11-4. Attempted TCP connection to closed port
Whether connecting to an open port or a closed port, only two packets
are required to determine whether the port is open or closed. In
addition, many operating systems do not log incoming connections if
the full three-way handshaking process has not completed. Half-open
scanning relies on the ability to create a TCP packet with the
SYN packet set, and on capturing return traffic from the destination system ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.