端口扫描

需要调试一个设备，可以还没有拿到手册，面对一个盒子束手无策。
突然想起来可以扫描设备的网络端口，于是搜索一番，找到nmap工具，果然尝试成功。
从扫描到的端口出发，虽然没有完全弄清楚设备的工作原理，但是获得很有价值的整体认识。

nmap

Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing. It was designed to rapidly scan large networks,
although it works fine against single hosts. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what
services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet
filters/firewalls are in use, and dozens of other characteristics. While Nmap is commonly used for security audits, many systems and network
administrators find it useful for routine tasks such as network inventory, managing service upgrade schedules, and monitoring host or service
uptime.

nmap -sT host/network

扫描host/network中开放的TCP端口。

nmap -sU host/network

扫描host/network中开放的UDP端口。

nmap -A host/network

aggressive扫描模式，是一个综合功能的命令，能得到host/network的多种信息。

netstat/ss

netstat是一个属于历史的命令了。ss用于输出socket statistics，可以替代netstat，查看本机的socket信息。
ss是登陆设备后使用的程序，能获得比nmap更详细的信息。