Key points of data link layer and network layer protocol

Catalog

Data link layer  

Point to point protocol PPP 

Network layer and IP agreement  

The network layer provides datagram Services

Address resolution protocol ARP

IP Layer forwarding packet flow  

  Divide subnets

Calculate the number of hosts in the subnet through the subnet mask 、 Number of subnets 、 Total number of hosts

Forwarding packets when using subnets   

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Private address ：

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Data link layer  

Point to point protocol PPP 

 

 

Network layer and IP agreement  

The network layer provides datagram Services

 

 

A Class address ：1.0.0.0-127.0.0.0

B Class address ：128.0.0.0-191.255.255.255

C Class address ：192.0.0.0-223.255.255.255

D Class address ：224.0.0.0-239.255.255.255

E Class address ：240.0.0.0-255.255.255.254

0.0.0.0 All zero address is ： Current host

255.255.255.255 whole 1 The address is ： The broadcast address of the current subnet

Address resolution protocol ARP

IP Layer forwarding packet flow  

  Divide subnets

Subnetting adds flexibility , But it reduces the total number of hosts that can connect to the network .

Calculate the number of hosts in the subnet through the subnet mask 、 Number of subnets 、 Total number of hosts

Prophet condition ： The subnet mask is also a 32 Digit number , Its corresponding IP All the bits in the network identification part of the address are "1", Corresponding IP The part of the address host ID is "0".

eg: Subnet mask ：255.255.224.0

——— Binary representation ：11111111.11111111.11100000.00000000

share 13 individual "0"

The number of hosts in the subnet ：2^13 - 2 = 8190

subtract 2 The reason is that ： All zero address is ： Current host

                            whole 1 The address is ： The broadcast address of the current subnet

Number of subnets ：

         Abandon 8 individual "0", more than 5 individual "0"(B Class address , So we need to give up 8 individual "0")

        256 / (2^5) = 8 perhaps B Class address removes the network flag 16 individual "1", Remnant 3 individual "1",2^3 = 8

Total number of hosts ：( The number of hosts in the subnet * Number of subnets )    8190 * 8 = 65024

eg1： It is known that IP The address is 141.14.72.24, The subnet mask is 255.255.192.0, Try to find the network address .

 

eg2： In the above example , If the subnet mask is changed to 255.255.224.0, Try to find the network address , The results of the discussion .

Different masks have different effects , The top two B Class address gets the same network address due to different subnet masks , But the maximum number of hosts in the subnet is different .

Be careful ： Any number and 255& The latter is itself , because 255 It's all. 1

Forwarding packets when using subnets   

Private address ：

Private address (private address) It's also called a private address , They will not be used around the world , Local significance only ( In LAN ).

 

    A Class private address ：10.0.0.0/8, The scope is ：10.0.0.0~10.255.255.255

 

    B Class private address ：172.16.0.0/12, The scope is ：172.16.0.0~172.31.255.255

 

    C Class private address ：192.168.0.0/16, The scope is ：192.168.0.0~192.168.255.255

contrast ：

A Class address ：1.0.0.0-127.0.0.0

B Class address ：128.0.0.0-191.255.255.255

C Class address ：192.0.0.0-223.255.255.255

D Class address ：224.0.0.0-239.255.255.255

E Class address ：240.0.0.0-255.255.255.254