Network model and protocol

A network model

One 、OSI Seven layer model

​ OSI Open System Interconnect Open Systems Interconnection model

​ effect : Reduce the complexity of network data communication , Easy troubleshooting

 application layer 
	 Providing applications / Software ,  The interface between people and the network  
	 Provide data 
 The presentation layer 
	 Responsible for data format conversion ,  Like compression / decompression 、 encryption 、 Decrypt 
 The session layer 
	 Establish a conversation 、 Maintain conversation 、 Disconnect session 
	 conversation :  Identify the login identity of the client ( Log in )
 Transport layer 
	 Provide end-to-end communication ,  Identify different applications  
	 Port number     1--65535
		 effect ： Identify different programs  
	windows View the command of the port   > netstat -an
 The network layer 
	 Typical equipment :  Router 
	 Provide network to network communication ,   The Internet --- Network segment  
	 Provide routing , according to IP Address for routing  
 Data link layer 
	 Typical equipment :  Switch 
	 Provide point-to-point communication 
	 rely on MAC Address ,  Physical address 
	windows see MAC Address ：  ipconfig /all 
	Linux see MAC Address :     ifconfig, ip addr show
 The physical layer 
	 Provide physical links  

Two 、TCP/IP Five layer model

 application layer 、 Transport layer 、 The network layer 、 Data link layer 、 The physical layer  

3、 ... and 、 Typical protocol

 application layer  

1、http  
	 Realization web The data transfer ,  Plaintext transmission  
	
2、https
	 Realization web The data transfer ,   Ciphertext transmission 
	
3、ftp   
	 File transfer protocol , Implement data sharing  
	
4、DNS
	 Realization IP Address 、 Host name resolution  
	
5、ntp
	 Network time protocol ,  Time synchronization  
	
6、snmp
	 Simple network management protocol ,  Implementation monitoring  

7、ssh
	 Device remote connection ,  Ciphertext transmission ;   Suitable for connecting to the server 
	
8、telnet
	 Device remote connection ,  Plaintext transmission ;   It is suitable for connecting network devices in LAN  

 Transport layer  

 One 、TCP	 Transmission control protocol  

1、 Connection oriented protocol 
	 Before sending data between hosts , Need to establish TCP Connect , After the connection is completed, the real data will be sent , After the data is sent , The connection between hosts will be disconnected  
	TCP The connection is two-way  
	
     Three handshakes , Establishing a connection  
        (a)  host A Host computer B Send with SYN Logo data , Indicates a request to establish a connection 
        (b)  host B Host computer A Send with ACK, SYN Logo data , Agree to establish a connection 、 towards A Send a connection request  
        (c)  host A Host computer B Send with ACK Logo data , Consent and B Establishing a connection  
2、 A reliable agreement 
	(a)  Retransmission timer  
	(b)  Sliding window mechanism , flow control , Avoid network congestion  
	
 Two 、UDP	 User datagram protocol  

1、 No connection protocol 
2、 An unreliable agreement 


 see TCP Protocol related ports 
[[email protected] ~]# netstat -antp 

 see UDP Protocol related ports  
[[email protected] ~]# netstat -anup 

 The network layer  

 One 、IP   Internet Protocol   Internet Protocol  

 Two 、ICMP agreement  
	 Internet control message protocol ,  Test network connectivity ; 
	ping Tools 

ping Tool use : 
	-c    Appoint ping The number of times 
	-s	  Appoint ping Packet size 
	
[[email protected] ~]# ping -s 4000 -c 5 192.168.65.1


 3、 ... and 、IGMP agreement  
	 Implement multicast  
	
	
 Four 、ARP agreement  
	 Address resolution protocol  
	 effect :  according to IP The address for MAC Address 

Four 、 Data encapsulation

 application layer ：  Generate data  
 Transport layer ： TCP/UDP Headlines 
	 Source port ,  For requesting data , It's usually >1024 The random port of 
	 Destination port 
 The network layer : IP Headlines 
	 Source IP Address 
	 Purpose IP Address 
 Data link layer : MAC Frame head 
	 Source MAC Address 
	 Purpose MAC Address 

5、 ... and 、 Static routing

 Add route 

route add -net  Destination segment   gw  Next hop address 

[[email protected] ~]# route add -net 192.168.2.0/24 gw 192.168.3.2
[[email protected] ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     0.0.0.0         255.255.255.0   U     100    0        0 ens33
192.168.2.0     192.168.3.2     255.255.255.0   UG    0      0        0 ens37
192.168.3.0     0.0.0.0         255.255.255.0   U     100    0        0 ens37



 Enable routing and forwarding   
[[email protected] ~]# echo 1 > /proc/sys/net/ipv4/ip_forward
[[email protected] ~]# cat /proc/sys/net/ipv4/ip_forward
1


 Set up Linux The host starts in character mode by default  
[[email protected] ~]# systemctl set-default multi-user.target