What is IPv6? What you don't know about IPv6 culture?

In the past ten years, IPv6 should have been greatly developed, but in fact, this good thing did not happen, which led to a result that most people did not understand the knowledge of IPv6: What is IPv6? What are the advantages and disadvantages? How to use it? Why does it exist? How is it different from iPv4? Do you know all this? The following is a detailed introduction.

What did IPv4 do wrong?

We have been using IPv4 since 198 1 published RFC79 1. At that time, computers were rarely big and expensive, and IPv4 claimed to provide 4 billion IP addresses. At that time, it seemed that this figure was huge. Unfortunately, so many 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, and the remaining 229 are occupied for future needs, so these idle addresses cannot serve the users who really need them because of the restrictions of network routing rules.

The final result is that the number that looks so big at 198 1 becomes so small at 20 14.

The Internet Engineering Task Force (IETF) pointed out this problem in the early 1990s and provided two solutions: Typeless Inter-domain Routing (CIDR) and Private IP Address.

Before CIDR appeared, you could only choose three network address lengths: 24 bits (* * 1 6,777, 2 14 available address), 20 bits (* *1048,574 available address), 16 bits (. After CIDR appeared, you can subdivide a network into multiple subnets.

For example, if you need 5 IP addresses, your ISP will provide you with a subnet with a 3-digit host address, which means you can get up to 6 addresses. —— Regardless of the network number of the subnet, the length of the 3-digit host address can represent 0 ~ 7 * * 8 addresses, but the 0th and 7th addresses have special purposes and cannot be used by users, so at most 6 addresses can be obtained).

This method allows 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 in it can access the hosts on the external network, but it is difficult for the hosts on the external network to access the hosts on the network you created, because your network is private and others can't see it.

You can create a very large network because you can use16,777,214 host addresses, and you can divide this network into smaller subnets for your own management.

Maybe you are using a private address now. Look at your IP address. If the address is within these ranges, it is10.0.0–10.255.255,172.438+06.0.0–15438+258+

These two schemes have effectively delayed the disaster of "IP address exhaustion" for a long time, but this is only a stopgap measure after all, and now we are facing the final trial.

Another problem with IPv4 is that the message header length of this protocol is variable.

If software is used to realize data routing, this problem is easy to say, but now the router functions are provided by hardware, and it is difficult for hardware to handle variable-length message headers. Large routers need to handle a large number of packets from all over the world. At this time, the load of the router is very large, so obviously, we need to fix the length of the message header.

There is another problem when assigning IP addresses. The Internet was invented by Americans (this evil capitalist country occupies a large number of IP addresses), and other countries only get fragments of IP addresses. We need to customize a new architecture, so that continuous IP addresses can be geographically distributed and the routing table will become smaller (think about it, the network speed is definitely faster).

Another problem, which you may not believe, is that IPv4 is difficult to configure and change. You may not encounter this problem, because your router has done these things for you, so you don't have to worry, but your ISP has been having a headache with this problem.

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

IPv6 and its advantages

IETF released the next generation IP address standard in199565438+February. The name is IPv6, why not IPv5? → _→ For some wrong reason, the number "Version 5" has been used by other projects. The advantages of IPv6 are as follows:

-128 bit address length (* * has 3.4023669× 10 addresses)

-The addresses under its architecture are logically aggregated.

-The header length is fixed.

-Support automatic configuration and modification of the network.

We analyze these characteristics one by one:

address

When people talk about IPv6, the first thing they notice is that it has many addresses. Why so many? Because designers consider that addresses can't be fully utilized, they must provide enough addresses for users to squander in order to achieve some special purposes.

So if you want to set up your own IPv6 network, your ISP can assign you a network with a 64-bit host address length (you can assign 1.44407× 10 host), and you can play whatever you want.

polymerize

With so many addresses, these addresses can be sparsely assigned to hosts, thus routing packets more effectively. Calculate an account, your ISP gets a network space with an address length of 80 bits, where 16 bits is the ISP's subnet address, and the remaining 64 bits are given to you as the host address. In this way, your ISP can allocate 65,534 subnets.

However, these address assignments are not immutable. If an ISP wants to have more subnets, it can do it (of course, a local ISP may ask for another 80-bit network space).

The highest 48-bit addresses are independent of each other, that is to say, although ISP and ISP may be assigned to the same 80-bit cyberspace, the two spaces are isolated from each other, and the advantage is that the addresses of a cyberspace will be aggregated.

Fixed message header length

The length of the IPv4 header is variable, but the length of the IPv6 header is fixed at 40 bytes. Because of the extra parameters, IPv4 will make the message header longer. If there are extra parameters in IPv6, the information will be placed next to the message header and will not be processed by the router. When the message arrives at the destination, the software will extract these additional parameters.

The IPv6 header has a part called "flow", which is a 20-bit pseudo-random number to simplify the routing process of the router to the packet. If there is a "flow" in a packet, the router can use this value as an index to find the routing table instead of slowly traversing the entire routing table to query the routing path. This advantage makes IPv6 easier to be routed.

Automatic configuration

In IPv6, when a host is turned on, it will check the local network to see if any other host uses its own IP address. If the address is not used, query the local IPv6 router and ask the IPv6 address after finding it. Then this host can connect to the Internet-it has its own IP address and its own default router.

If this default router fails, the host will find another router as a backup router. This function is difficult to realize in IPv4 protocol. Similarly, if the router wants to change its address, just change it yourself. The host will automatically search for the router and automatically update the router address. Routers keep both old and new addresses until all hosts update their router addresses to the new ones.

Automatic configuration of IPv6 is not a complete solution. In order to use the internet effectively, the host needs other things: domain name server, time synchronization server or file server. So dhcp6 appeared, providing the same service as dhcp. The only difference is that the machine of dhcp6 can be started in a routable state, and a dhcp process can provide services for a large number of networks.

The only big problem is

If IPv6 is so much better than IPv4, why isn't it widely used? 20 14 in may, Google estimated that the market share of IPv6 was 4%. One of the most basic reasons is that "the chicken or the egg came first". Service providers want their servers to serve as many customers as possible, which means they must deploy IPv4 addresses.

Of course, they can use IPv4 and IPv6 addresses, but few customers will use IPv6. You need to make some minor changes to your software to adapt to IPv6.

Another headache is that many home routers don't support IPv6 at all. In addition, ISP is unwilling to support IPv6.

I asked my ISP this question, and the answer is: Only when customers explicitly indicate that they want to deploy this, will they use IPv6. Then I asked how many people have this demand now, and the answer was: including me, * * * yes 1.

In stark contrast to this reality, all mainstream operating systems such as Windows, OS and Linux have supported IPv6 by default for many years. These operating systems even provide software to cover IPv6 packets with IPv4, so as to fool those hosts that will discard IPv6 packets, thus achieving the purpose of data transmission.

Full text abstract

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 joining the network for the first time.

The problem is that the public is slow to accept and use IPv6, because the cost of change is too high.

The good news is that all operating systems support IPv6, so when you want to make changes one day, your computer can switch to the new architecture with a little change.

? Monitor the dead chain? /b/slj/