Summary of some network knowledge (for personal use)

1. Base conversion

Converting all bases to decimal is to convert literal value * weight

For example, if the hexadecimal 5AEF is converted into a 10-digit system, it will be 1* 15+16 14+32 10+64 * 5

2. The concept of IP address network segment, available IP, broadcast address

比如一个ip为10.1.1.1/24

那么他的网络号就是前24位，主机号就是后8位

他的子网掩码就是255.255.255.0

他的网段就是10.1.1.0

他的可用IP有256-2=254个

主机号全为1的是广播地址，不可用
主机号全为0的是网段号，不可用
其余的都是可用ip

3. Classification of IP addresses, default subnet mask

A类：1-126     默认⼦⽹掩码：255.0.0.0=/8
B类：128-191   默认⼦⽹掩码：255.255.0.0=/16
C类：192-223   默认⼦⽹掩码：255.255.255.0=/24
D类：224-239   组播地址（普通计算机⽆法使⽤
E类：240-254   科研使⽤（普通计算机⽆法使⽤

⽬前我们可以使⽤的只有A、B、C 3类
ABC3类的⼦⽹掩码可以修改
少个0 是因为0可以代表任意ip或者是无效ip
少个127 是因为127代表自己 
少个255  是因为被用来当作子网掩码了

4.vlsm borrowing method and common heterogeneous subnet masks

vlsm: variable length subnet mask

因：IPV4地址不够⽤，才有VLSM技术延缓地址不够⽤，同时启⽤NAT技术延缓地址不够⽤

也是32位

10.1.1.1/25
那就是
10.1.1.0 xxxxxxx/25
10.1.1.1 xxxxxxx/25
这个25是转化成2进制后不变的位数

异类子网掩码
255.255.255.0 /24
255.255.255.128 /25
255.255.255.192 /26
255.255.255.224 /27
255.255.255.

5.vmware network architecture

6. Management of users and groups

whoami      #查看当前的用户
whoami /user   #可以查看当前用户和对应的SID
net user     #查看用户列表
net user ⽤户名 密码    #改密码
net user ⽤户名 密码 /add #创建⼀个新⽤户
net user ⽤户名 /del #删除⼀个⽤户
net user ⽤户名 /active:yes/no #激活或禁⽤账户

查看电脑用户、组的方法：
到计算机管理里面看

After creating a new user, use it to log in, and Windows will automatically create a home directory for him, which is the user directory on the C drive.
When a user belongs to multiple groups at the same time, permissions are cumulative.
Sharing permissions are taken by intersection.

NTFS permissions

By setting NTFS permissions, different users can have different permissions on file access.

ntfs is a file system

There are three types of file systems:

FAT32 windows
NTFS windows
EXT5 linux common

Among them, only the ntfs file system can set permissions!

7. Common port numbers and protocols

SMB  445    共享文件
FTP  20/21  文件传输
ssh   22    远程桌面管理    
telnet  23  远程桌面管理
RDP   3389  远程桌面管理  使用命令：mstsc
dns   53    ip和域名的转换
dhcp  67/68  为主机分配ip

8. Essential knowledge

User-unique value: SID whoami/user

File where user passwords are stored: C\windows\sysytem32\config\SAM

Windows built-in accounts: administrator, guest, system, local service, network service

List several built-in groups: administrators, users, remote desktop, users, print

Command to change user password: net user student 123.com

Command to add user password: net user student 123.com /add

Hide share: sharename$

net share displays shared files

net share xxx/del