June 2020
Intermediate to advanced
423 pages
7h 58m
Chinese
Content preview from Kali Linux学习手册
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120
｜
第
3
章
器接收传入的数据包，并根据
4
元组信息（源和目标
IP
地址以及端口）确定
应用程序正在等待该数据包。
由于两种传输协议之间存在差异，因此扫描的工作原理不同。最后，你正在
寻找开放的端口，但确定信息的方法是不同的。
Kali Linux
附带了一些端口扫
描工具。端口扫描事实上的标准工具是
nmap
，因此我们首先会使用它，然后
介绍其他用于高速扫描的工具，以及高效扫描大型网络的工具。
TCP
扫描
TCP
是一种面向连接的协议。因为它是面向连接的，这意味着会对会话的两
端进行跟踪，可以认为通信是有保障的。但是，这种保障只是针对受控的两
个端点。如果两个系统之间的网络中发生了某些事情，那么就无法确保通信
能够正常进行，但是可以保证告知用户传输何时失败。此外，如果端点的接
收方没有收到传输数据，发送方将会知道。
由于
TCP
是面向连接的，因此它使用三次握手来建立连接。
TCP
端口扫描通
常会利用该握手来确定端口是否打开。如果
SYN
消息（三次握手的开始）被
发送到服务器并且端口打开，则服务器将使用
SYN/ACK
消息进行响应。如
果端口未打开，服务器将发送
RST
（重置）消息进行响应，该消息指示发送
系统应该停机并且不再发送任何消息。这清楚地告知发送系统该端口不可用。
任何端口扫描的挑战，特别是对于最重要
TCP
来说，都是防火墙或是其他端
口阻塞机制。发送消息时，防火墙或访问控制列表可以阻塞消息通过。这可
能使得发送主机处于不确定的状态。没有响应并不表示端口被打开或关闭，
因为如果防火墙或访问控制列表只是将入站消息丢弃，那么根本就没有响应。 ...
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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.