IPv6: Why do I have to make up for IPv4 errors!

IPv6: Why do I have to make up for IPv4 errors!

In the past ten years, IPv6 has been expected to develop a lot, but in fact this kind of good thing has not come, leading to a result, that is, most people do not know some knowledge about IPv6: What is it? How to use it? Why does it exist?

What does IPv4 do wrong?

We have been using IPv4 since the RFC791 standard was released in 1981. At that time, the computer was too big and expensive, but IPv4 claimed to be able to provide 4 billion IP addresses. At that time, this number was very big.

Unfortunately, these IP addresses are not fully utilized, and there is a gap between them.

For example, a company may have 254 (28-2) addresses, but only 25 of them are used. The remaining 229 are empty for future use, therefore, these idle addresses cannot serve users who really need them, because they are limited by network routing rules.

The final result is the big, big, and small figure in.

The Internet Engineering Task Group (IETF) pointed out this problem in Early 1990s and provided two solutions: classless Inter-Domain Routing (CIDR) and private IP address.

Before CIDR appears, you can select only three network address lengths: 24 bits (16,777,214 available addresses in total) and 20 bits (1,048,574 available addresses in total) and 16-bit (65,534 available addresses in total ). After the emergence of CIDR, you can divide a network into multiple subnets.

For example, if you need five IP addresses, your ISP will provide you with a subnet where the host address length is 3 bits, that is, you can get up to six addresses. -- Aside from the subnet network number, the length of the three host addresses can be 0 ~ There are 8 addresses in total, but 0th and 7th have special purposes and cannot be used by users, so you can get up to 6 addresses ).

This method allows the ISP to allocate IP addresses as efficiently as possible. The effect of the "private address" solution is that you can create a network by yourself, and the hosts inside can access the hosts on the Internet, however, it is difficult for an Internet host to access the host on the network you created, because your network is private and invisible to others.

You can create a very large network, because you can use 16,777,214 host addresses, and you can divide the network into smaller subnets for easy management.

Maybe you are using a private address. Check your own IP address. If the IP address is in the range of 10.0.0.0-10.255.255.255.255, 172.16.0.0-172.31.255.255, or 192.168.0.0-192.168.255.255, you are using a private IP address.

These two solutions have effectively delayed the disaster of "using up IP addresses" for a long time, but after all, this is only an alternative. Now we are facing a final trial.

There is another problem with IPv4, that is, the message header length of this protocol is variable.

If data routing is implemented through software, this problem is okay, but now the router functions are provided by hardware. It is difficult for hardware to process long message headers. A large router needs to process a large number of data packets from all over the world. In this case, the load on the router is very large, so it is obvious that we need to fix the length of the message header.

While allocating IP addresses, there is another problem: the Internet was invented by Americans (this evil capitalist country occupies a large number of IP addresses), and other countries only had to fragmentation of IP addresses. We need to re-customize an architecture so that continuous IP addresses can be centrally distributed in geographical locations, so that the route table can be smaller (think about it, the network speed must be faster ).

Another problem is that it may sound hard to believe that IPv4 configuration is difficult and cannot be changed. You may not encounter this problem because your router has done these things for you and you don't have to worry about it, but your ISP has always been a headache.

The next generation of Internet needs to consider all the above issues.

IPv6 and its advantages

In December 1995, IETF announced the next-generation IP address standard called IPv6. Why is it not IPv5? → _ → Due to an error, "version 5" is used by other projects. IPv6 has the following advantages:

-128-bit address length (3.402823669x10 characters in length)

-Logically aggregated addresses in the architecture

-Fixed Message Header Length

-Supports automatic configuration and modification of your network

We analyze these features one by one:

Address

When we talk about IPv6, the first thing we notice is that it has a lot of addresses. Why? Because the designer considers that the address cannot be fully utilized, we must provide enough addresses for users to bid for some special purposes.

So if you want to set up your own IPv6 network, your ISP can allocate a network with a 64-bit host address length (1.844674407*10 hosts can be allocated ), you can play it as you want.

Aggregation

With so many addresses, these addresses can be evenly allocated to the host to route data packets more efficiently. Assume that your ISP has an 80-bit address length network space. The 16-bit is the ISP's subnet address, and the remaining 64-bit is assigned to you as the host address. In this way, your ISP can allocate 65,534 subnets.

However, the allocation of these addresses is not static. If the ISP wants to have more small subnets, it can be done completely (of course, the local ISP may require an 80-bit network space ).

The maximum 48-bit addresses are independent from each other. That is to say, although the ISP and ISP may be allocated 80-bit network space in the same region, the two spaces are isolated from each other, the advantage is that the addresses in a network space are aggregated.

Fixed Message Header Length

The length of an IPv4 message header is variable, but the length of an IPv6 message header is fixed to 40 bytes. IPv4 will cause the message header to become longer due to additional parameters. If there are additional parameters in IPv6, the information will be placed in a place next to the message header and will not be processed by the router, when a message reaches its destination, these additional parameters are extracted by the software.

The IPv6 message header is called "flow" and is a 20-bit pseudo-random number, which is used to simplify the router's routing of data packets. If a data packet contains a "flow", the router can search the route table based on this value as an index, without having to traverse the entire route table to query the route path. This advantage makes IPv6.

Automatic Configuration

In IPv6, when the host is started, it checks the local network to see if other hosts use their own IP addresses. If the address is not used, query the local IPv6 router and request an IPv6 address from it. Then the host can be connected to the Internet-it has its own IP address and its default router.

If this default router goes down, the host will find another router as a backup router. This function is very difficult to implement in the IPv4 protocol. Similarly, if the vro wants to change its own address, just change it. The host automatically searches for the vro and updates the vro address. The router saves the New and Old addresses at the same time until all hosts update their own vro addresses to new addresses.

Automatic IPv6 Configuration is not a complete solution. To effectively use the Internet, another thing is required for a host: a Domain Name Server, a time synchronization server, or a file server. As a result, dhcp6 emerged to provide the same services as dhcp. The only difference is that dhcp6 machines can be started in a routable state, and a dhcp process can provide services for a large number of networks.

The only big problem

If IPv6 is much better than IPv4, why is it not widely used? Google estimated IPv6 market share to be May 2014 in 4%. The most basic reason is "first chicken or first egg ".

Service providers want their servers to provide services to as many customers as possible, which means they must deploy an IPv4 address.

Of course, they can use both IPv4 and IPv6 addresses, but few customers will use IPv6, and you also need to make some small changes to your software to adapt to IPv6.

Another headache is that many home routers do not support IPv6.

In addition, ISP does not want to support IPv6.

I asked my ISP this question and got the answer: only when the customer explicitly points out that they want to deploy the service will IPv6 be used. Then I asked how many people have this need. The answer is: I have one in total.

Obviously, all mainstream operating systems Windows, OS, and Linux support IPv6 by default for many years. These operating systems even provide software to put IPv6 data packets on IPv4 to cheat hosts that discard IPv6 data packets so as to transmit data.

Summary

IPv4 has served us for a long time, but its defects will encounter insurmountable difficulties in the near future. IPv6 can solve this problem perfectly by changing the Address Allocation Rules, simplifying the packet routing process, and simplifying the configuration process when the network is first added.

The problem is that the public is slow in accepting and using IPv6, because the change is too costly.

The good news is that all operating systems support IPv6. so when you want to make a change one day, your computer only needs to change a little bit and you will be able to switch to a new architecture.