The Foundation of computer Network (1)-- A brief introduction to the reference Model of Network Communication and IP address

I. reference model of network communication

OSI model:

Application layer: an interface between network services and end users

Presentation layer: data representation, security, compression

Session layer: establish, manage, and terminate a session

Transport layer: defines the protocol port number over which data is transmitted, as well as control and error checking

Network layer: logical address addressing to achieve path selection between different networks

Data link layer: functions such as establishing logical connection, hardware address addressing, error checking, etc.

Physical layer: establish, maintain, disconnect physical connection

TCP/IP model

TCP/IP five-tier model:

Application layer Transport layer Network layer data Link layer physical layer TCP/IP four-layer Model: application layer

Transport layer

Network layer network interface layer

2. Network cable

1, definition: 8 copper wires, in pairs, a total of four pairs, are all wound together at a certain angle, so the network wire also becomes a "twisted pair".

2. Network cable classification:

(1) based on transmission speed and anti-jamming ability, it can be divided into 5 categories, super 5 categories, 6 categories and 7 categories:

Category 5: 100Mbps

More than 5 categories (5e): 100Mbps

Category 6: 1000Mbps

(2) based on the line order, the network cable can be divided into:

Straight-through line: the line order on both sides is the same (when connecting different devices)

Crossed lines: different lines on both sides (when the same device is connected)

Reverse line: the order of the lines on both sides is completely opposite.

3. The wire sequence of the network cable:

Standard-568B: White orange, orange, white-green, blue, white-blue, green, white-brown, brown

Standard-568A: White green, green, white orange, blue, white blue, orange, white brown, brown

(difference: 1, 3, 2, 6)

Note: the reason why the crossing line is used to connect the same equipment:

Take PC as an example: the network card / port of each PC is fixed, port 1 and 2 are responsible for sending information, and port 3 and 6 are responsible for receiving information, so cross lines are needed for the connection between PCs. On the other hand, the network ports 1 and 2 of the router are responsible for receiving information, and ports 3 and 6 are responsible for sending information, so the router and PC should be connected by a straight line.

III. Brief introduction of TCP/IP protocol

TCP/IP is the most widely supported set of communication protocols

-including standard protocols in a large number of Internet applications

-support for communication across network architectures / operating system platforms

Three elements of communication between host and host

-IP address

-Subnet mask

-IP routing

1.ip address introduction

All devices that can surf the Internet must have an IP address. Every IP address means that everyone must have a name.

What the common IP address looks like: for example, the default address of TP-Link unlimited route: 192.168.1.1

Note: the IP address must be paired with the subnet mask, otherwise it is meaningless.

Check the IP address configuration of your Nic:

Click start-> run-> enter cmd to invoke the "Command Line window" (Quick call run: keyboard start key + r)

Enter the command in the command line window: ipconfig / / display the IP address information of the network card

Or: ipconfig / all / / View all the information of all the network cards of the device

two。 Connectivity testing tool-ping

How it works:

(1) send a "request packet"-request to the specified destination IP address

(2) the target device returns a "reply package"-reply

For example: ping succeeded!

PC > ping 192.168.1.2

Pinging 192.168.1.2 with 32 bytes of data:

Reply from 192.168.1.2: bytes=32 time=0ms TTL=128

Reply from 192.168.1.2: bytes=32 time=0ms TTL=128

Reply from 192.168.1.2: bytes=32 time=0ms TTL=128

Reply from 192.168.1.2: bytes=32 time=0ms TTL=128

Ping statistics for 192.168.1.2:

Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)

Approximate round trip times in milli-seconds:

Minimum = 0ms, Maximum = 0ms, Average = 0ms

For example: ping failed!

PC > ping 192.168.1.3

Pinging 192.168.1.3 with 32 bytes of data:

Request timed out. (default timeout is 2s=2000ms)

Request timed out.

Request timed out.

Request timed out.

Ping statistics for 192.168.1.3:

Packets: Sent = 4, Received = 0, Lost = 4 (100% loss)

Reason for failure:

-the target may turn on the firewall

-two hosts are not connected to the same virtual network

Solution:

-- check and turn off the target host firewall

-- check whether two hosts are bridged to the same virtual network

Shortcut commands:

Press ctrl and c at the same time to quickly terminate the ping command

Special ping commands:

Ping 127.0.0.1

# the address represents the device itself

# this command indicates that you can send a packet to yourself; if it is passed, you can receive and send messages normally.

Usually use this command to check whether the network card / port function of the device itself is normal.

Problem: users find that the host can access QQ but cannot access Baidu website

Analyze the reason: DNS cannot resolve domain name

Solution: ping www.baidu.com test whether ping can be reached, if not ping, then check whether the local DNS server address configuration is correct.