Computer network (1)-----Network layer IP Protocol overview

Network layer
Concept

The network layer is the third layer in the OSI Reference Model, which is between the transport layer and the data link layer, and it further manages the data communication in the network between the two adjacent endpoints provided by the data link layer, and tries to transfer the data from the source side to the destination through several intermediate nodes. This provides the most basic end-to-end data transfer service to the transport layer.

Objective

The purpose of the network layer is to realize the transparent transfer of data between two end systems, including addressing and routing , establishing, maintaining and terminating the connection . It provides services that do not require the transport layer to understand the data transfer and switching technologies in the network.

Characteristics

The network layer only provides a simple, flexible, non-connected, best-effort delivery of packet services.

Classification of IP addresses

IP Address composition: network number (Net-id) + host number (Host-id). where the IP address is divided into a,b,c,d,e five categories.

Class A address: network Address (1Byte) + host address (3Byte), and the first network address must be 0; The value range of the network address is 0~~127,

While 0 is reserved and represents all IP addresses, 127 is also the reserved address and is used for testing loopback ( native ). So the range of Class A addresses is actually from 1-126.

There are 126 available Class A networks, each of which can hold more than 100 million hosts (2 of the 24-minus 1 hosts).

　　Class A IP range : the first is 0;1.0.0.1~~126.255.255.254; host number 24 bit

Class B Address: network Address (2Byte) + host address (2Byte), and the network address of the first two bits is 10; The range of the network address is 128~~191,

The available class B networks are 2 of 14, and each network can hold more than 60,000 hosts (2 16-time minus 0 and broadcast addresses).

　　Class B IP range : The first two bits are 10; 128.0.0.1~~191.255.255.254; host number 16 bit

C class Address: network Address (3Byte) + host address (1Byte), and the network address of the first three bits is 110; The range of the network address is 192~~223,

The available Class C network has 2 of 21, up to 2.09 million, each network can accommodate 254 hosts.

　　Class C IP range : The first three bits are 110;192.0.0.1~~223.255.255.254; Host number 8 bit

Class D Address: This type of address is called a multicast address, also known as the multicast address, the first four bits must be 1110; The range of the network address is 224~~239,

　　Class D IP range : The first four bits are 1110;224.0.0.1~~239.255.255.254

Class E Address: This type of address is reserved for future use, the first five digits must be 11110; The range of the network address is 240~~254,

　　Class E IP range : The first five bits are 11110;240.0.0.1~~254.255.255.254

Resources

Http://www.cnblogs.com/xiehy/p/3460766.html

Computer network (1)-----Network layer IP Protocol overview