[try to hack] IP address

Blog home page ： Happy star The blog home page of
Series column ：Try to Hack
Welcome to focus on the likes collection ️ Leaving a message.
Starting time ：2022 year 6 month 18 Japan
The author's level is very limited , If an error is found , Please let me know , thank ！

A lot of content comes from This article , Only for your own study
More about subnet addressing , see This article

ip Address Overview

IP The address is and the length is 32 bit, from 4 Byte composition . For the convenience of reading and writing ,IP Addresses are usually expressed in dotted decimal numbers .

IPv4 Address range
00000000.00000000.00000000.00000000~11111111.11111111.11111111.11111111, namely 0.0.0.0~255.255.255.255

Subnet mask

LAN communication rules ：
In the same LAN , all IP You must be in the same network segment to communicate with each other ！

IP Address structure ：
Network bit + Host bit （ The network bits are the same IP Address , For the same segment ）

Subnet mask ：
Used to determine IP Network bit of address

How does the subnet mask confirm the network bit ：
And 255 The corresponding number is network bit , And 0 The corresponding number is the host bit

One IP The address must have a subnet mask （ There is a default subnet mask, such as C The subnet mask of the segment is /24）

Subnet mask and ip The address is similar to , It's also 32 Bit binary number
Subnet mask, for example ：255.255.255.0

Another representation of subnet mask ：192.168.1.1/24
among 24 Indicates the first in the subnet mask 24 Position as 1

Classified addressing

In the length of 32 Bit IPv4 In the address , There is a continuous bit called the network number , There is also a continuous bit called the host number .

A class ： The network number is 8 position , The host number is 24 position
B class ： The network number is 16 position , The host number is 16 position
C class ： The network number is 24 position , The host number is 8 position
Ａ、Ｂ、Ｃ The three types of subnet masks can be modified

Small exercise ：
ip Address 10.1.1.1
Subnet mask 255.255.0.0
ask ：10.1.1.1 Which network segment does it belong to ？ How many are available in the network segment IP Address ？ What is the broadcast address of this network segment ？
answer ：
10.1.1.1 Belong to 10.1.0.0 Network segment
Network segment IP Number of addresses ：65534（10.1.0.1-10.1.255.254）
The broadcast address of this network segment is ：10.1.255.255

special IP Address

Public network IP Address ：IP Address by IANA Uniformly distributed , To ensure that any one IP The address in Internet The uniqueness on the Internet . there IP Address refers to the public network IP Address .

The private network IP Address ： In fact, some networks do not need to be connected to Internet, For example, the network in a closed laboratory of a University , As long as the network equipment in the same network IP The address does not conflict . stay IP In the address space ,A、B、C Some of the three types of addresses are reserved for the above situation , It's called private network IP Address .
A class ：10.0.0.0~10.255.255.255
B class ：172.10.0.0~172.31.255.255
C class ：192.168.0.0~192.168.255.255

255.255.255.255
This address is called a limited broadcast address , It can be used as a IP The purpose of the message IP Address using .
The router received the destination IP The broadcast address is limited IP After the message , Will stop thinking about this IP Forwarding of messages .

0.0.0.0
If you take this address as the network address , It means “ Any network ” Network address of ; If you use this address as the host interface address , It means “ Host interface on this network ” Of IP Address .
for example ： When a host interface has not obtained its own during startup IP Address time , You can send the destination to the network IP The address is limited broadcast address 、 Source IP The address is 0.0.0.0 Of DHCP Request message , hope DHCP After the server receives its own request , Be able to assign one to yourself IP Address .

127.0.0.0/8
This address is the loopback address , It can be used as a IP The purpose of the message IP Address using . Its function is to test the software system of the equipment itself .
Produced by a device 、 Purpose IP The address is the loopback address IP It is impossible for the message to leave the device itself .

169.254.0.0/16
If a network device gets IP The address mode is set to automatic acquisition mode , But the device did not find any available on the network DHCP The server , Then the device will use 169.254.0.0/16 A certain address of the network segment for temporary communication .
notes ：DHCP (Dynamic Host Configuration Protocol), Dynamic Host Configuration Protocol , Used to dynamically allocate network configuration parameters , Such as IP Address .

gateway

gateway ： An exit to the network ,Gateway=GW, The general gateway is on the router
Router ： You can use devices connected to the internal and external network

The router intranet interface must also be equipped with a IP, And the default address is the first or last of all available addresses （ No matter which enterprise in the world , All LANs ）, namely X.X.X.1 or X.X.X.254
（ This is why host discovery , The host number is too high or too low ）

The router in the figure 192.168.0.1 It is called the outlet of the intranet , It's a level . This IP It is called gateway .

PC If you want to communicate between, you must ensure that you are in the same network segment

a PC Want to access another PC The psychological activities of ：
（1） Compare whether they are in the same network segment ;
（2） If you are in the same network segment , Then send it directly , Instead of finding the gateway ;
（3） If not in the same network segment , Then contract directly to the gateway .