What is a legal IP address

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Among the legal IP addresses, Each three-digit number is between 0 and 254. It cannot be greater than 254, not even 255. This is a legal IP address, and IP addresses include Class A\B\C IP.

The IP addresses of iPv4 are all in the format of (1~255).(0~255).(0~255).(0~255).

The IP address range of Class A is 0.0.0.0-127.255.255.255

The IP address range of Class B is 128.0.0.0-191.255 .255.255

The IP address range of Class C is 192.0.0.0-223.255.255.255.

In a Class A IP address, the network identification length is 8 bits, the host identification length is 24 bits, and the subnet mask is 255.0.0.0. Class B is suitable for medium-sized networks.

The network identification length is 16 bits, the host identification length is 16 bits, and the subnet mask is 255.255.0.0. Class C is suitable for small-scale local area networks, in which the network identification length is 24 bits, the host identification length is 8 bits, and the subnet mask is 255.255.255.0.

Furthermore, in each legal IP address, there are four three-digit numbers separated by ".", and each three-digit number is between 0 and 255, and contains the number 255. .

Extension information:

Extension of IP address:

The existing Internet runs on the basis of the IPv4 protocol. IPv6 is the next version of the Internet protocol, which can also be said to be the protocol of the next generation of Internet. It was originally proposed because with the rapid development of the Internet, the limited address space defined by IPv4 will be exhausted, and the shortage of address space will inevitably hinder the further development of the Internet.

In order to expand the address space, it is planned to redefine the address space through IPv6. IPv4 uses a 32-bit address length, and there are only about 4.3 billion addresses, which are estimated to be allocated between 2005 and 2010, while IPv6 uses a 128-bit address length, which can provide almost unlimited addresses.

Based on a conservative estimate of the actual addresses that can be allocated to IPv6, more than 1,000 addresses can still be allocated per square meter of the entire earth. In the design process of IPv6, in addition to solving the address shortage problem, other problems that were not solved well in IPv4 were also considered, mainly including end-to-end IP connection, quality of service (QoS), security, multicast, and mobility. , plug and play, etc.

Compared with IPv4, IPv6 mainly has the following advantages.

First, the address space is significantly expanded. IPv6 uses a 128-bit address length to provide an almost unlimited number of IP addresses, ensuring the possibility of end-to-end connectivity.

Second, it improves the overall throughput of the network. Since IPv6 data packets can far exceed 64k bytes, applications can take advantage of the maximum transmission unit (MTU) to obtain faster and more reliable data transmission. At the same time, the routing structure is improved in design and simplified header length is adopted. Structure and a more reasonable segmentation method enable routers to speed up data packet processing and improve forwarding efficiency, thus improving the overall throughput of the network.

Third, the overall service quality has been greatly improved. The service level and flow tag in the header can realize priority control and QoS guarantee through router configuration, thus greatly improving the quality of IPv6 service. Fourth, security is better guaranteed. The use of IPSec can provide effective end-to-end security guarantees for upper-layer protocols and applications, and can improve security at the router level.

Fifth, support plug-and-play and mobility. When the device is connected to the network, it can automatically obtain the IP address and necessary parameters through automatic configuration, achieving plug-and-play, simplifying network management and easily supporting mobile nodes. And IPv6 not only borrows many concepts and terminology from IPv4, it also defines many new features required to move IPv6.

Sixth, the multicast function is better realized. The "scope" and "flag" are added to the multicast function of IPv6, which limits the routing range and can distinguish between permanent and temporary addresses, which is more conducive to the implementation of the multicast function.

With the rapid development of the Internet and the continuous improvement of Internet users’ requirements for service levels, IPv6 will receive more and more attention around the world. In fact, there is no rush to promote IPv6. The problem of insufficient IPv4 addresses can be solved by simply extending 32 bits from 8 to 40 bits based on the existing IPv4. In this way, the number of available addresses is expanded by 256 times.

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