Computer network Learning Notes--IP address and subnet of network layer

IPV4 Address:

We know that at the network layer (the Internet layer of TCP/IP architecture), one of the most important protocols is IP protocol, is now in the IPV4 and IPv6 transition period, but at present, IPV4 is still mainstream, so the main Ipv4.

Basic IP Address format:

The format of the internal IP address of the computer is represented by a 32-bit binary number, in order to make people seem convenient, usually using dotted decimal to represent the IP address, such as 192.168.1.25, which is used to separate the points of each paragraph, but also for the convenience of people to read the addition, the computer does not have this point inside.

Public IP address and private network IP address:

　　　　　　public IP address refers to the network can be directly used on the network, directly routed, and need to IP address management Agency (China to apply for IP address through APNIC) application, registration, purchase, and the world's only Ipv4 address.

　　　　　　A private IP address is a IPV4 address that can be used only within each user's own LAN and can be reused by different users without the need to request a purchase.

Subnet Mask:

The subnet mask is not an address, it is used to determine which part of an IP address is the network ID, which part is the host ID, the portion of a continuous 1 represents the network ID, and a continuous portion of 0 represents the host ID. For example, the first 24 bits of Class C network are the network number and the last 8 bits are the host number. Then the subnet mask of the C-class network is 255.255.255.0

Classification of IP addresses:

This classification is a comparative basis of knowledge, not in detail, here the main emphasis on the Class D network. Class D IP address belongs to the multicast address, and multiprocessing multicast address, with IP multicast technology can effectively solve the single point of transmission, multi-point receiving problem, can save bandwidth to reduce network load such as online live, Network TV and other services are based on the multicast characteristics of the network.

The scope of the entire class D IP address is 224.0.0.0~239.255.255.255. According to the different application environment and use is divided into four categories:

　　　　1. Reserved multicast address (224.0.0.0~224.0.0.255): These IP addresses are not assigned to specific users, and are primarily allocated to multicast routing protocols. IP packets that use this multicast address are not forwarded by the router.

2. Public multicast address (224.0.1.0~224.0.1.255): These multicast addresses are available worldwide and can be used directly on the Internet, as well as applications and purchases.

3. Temporary multicast address (224.0.2.0~238.255.255.255): is a multicast address used by enterprise users within the intranet, only valid on local LAN. Just like a private IP address.

4 Local Management multicast address (239.0.0.0~239.255.255.255): reserved for use in LAN internal multicast testing. Valid only on a specific local scope.

There are class nets and no-class nets:

In front of the IP address is divided into five categories of ABCDE, this network is called a class network , or standard network .

In order to solve the lack of IP address, there has been a VLSM (below) technology, the use of VLSM Technology division of the network is called the non-class network .

Network address, host address, broadcast address:

　　　　Network Address : The address used to identify a network, which is the first IP address in the class network or subnet, which is the IP address of the host ID section, which is all 0. As in 192.168.2.0, the Class C network, 192.168.2.0 is the network address.

　　　　broadcast address : is the last IP address in a network, that is, the host ID part is all 1 IP address, such as in 192.168.2.0 this class C network, 192.168.2.255, is the broadcast address of the network, using this address can be broadcast communication, Enables all nodes of the network to receive the same packet.

　　　　host address : In addition to the network address, broadcast address this one end of the ground, the other is the host address.

A few special IP addresses:1: Private IP address (LAN dedicated IP address): The purpose is to improve the reuse of IP addresses.

　　　　　　　　Class A: 10.0.0.0-10.255.255.255

Class B: 172.16.0.0-172.31.255.255

Class C: 192.168.0.0-192.168.255.255

2:169.254.0.0/16: In Windows system, if you set the automatic acquisition of IP address, the local network is not deployed to automatically obtain the IP address of the DHCP server, the host will automatically get a network segment IP address, this is called Automatic Private IP address .3:127.0.0.1: The native address, also known as the loopback address.4:0.0.0.0: Not a real IP address, it represents a collection: all unclear hosts and destination networks.Division and aggregation of IP subnets　　　VLSM (variable eldest son netmask) technology:

In order to solve the shortage of IPv4 address, the birth of this technology, VLSM for the division of the subnet. Divide a large network into small subnets. The basic idea is that the network ID portion of the IP address of the original class network is borrow as part of the host ID, so that it becomes part of the network ID (called the subnet ID). , the length of the host IP part is reduced, that is, the total number of hosts in the corresponding network (the total number of addresses) decreased, but this is not the purpose of VLSM, more crucially, it can be used flexibly based on the actual needs to adjust the size of the sub-network.

Note: In this way the subnet is divided into subnets, all 0 subnets, and all 1 subnets are available.

CIDR (No-class inter-Domain routing protocol):

The non-class inter-domain routing protocol allows multiple classes to be merged into a larger network, called a hyper-net.

For example, the 192.24,8.0~192.24.15.0 these 8 have a class network, you can synthesize a network number of 192.24.8.0, the subnet mask is 255.255.248.0.

CIDR can significantly reduce the number of table entries in the route table. For example, in the previous example, the 8 routes were reduced to 1 routes, which became a route aggregation.

By introducing CIDR, plus the subnet mask, the network number can now be seen as having no boundaries, that is, no class,

NAT (network address translation) technology:

The two technical vlsm and CIDR described in the front are fully leveraging the IPV4 address by adjusting the length of the subnet mask, while NAT technology allows the internal network (the network where the user is currently located) The private IP address is translated into a public IP address via address translation to access the Internet.nat service on the router.

about how the specific NAT works, this article is relatively good, you can take a closer look: Http://www.tuicool.com/articles/7JFZziM

　　　

Special IP Address:

　　　

Computer network Learning Notes--IP address and subnet of network layer