Build your own smart DNS with bind

China's North-South network problem is the heart disease of many website users. In addition to using dual-connect or multi-connect data centers, users can also use multiple image servers to speed up access. However, if the dual-pass data center is not a single IP address or multiple images are used, many images will face the first issue of multiple different Server IP addresses. China's North-South network problem is a heart disease for many people who do websites
In addition to dual-connection or multi-connection data centers, you can use multiple backup Storages to speed up user access.
However, if the dual-pass data center is not a single IP address or multiple images are used, the server IP address may be different.
At the earliest days, many image servers used different domain names, such as www1 and www2, or www and c. Nc
This method is unfriendly to users and inconvenient for promotion. For example, if you want to tell a friend a website and ask him what line he wants to give it to the website, or you may not know that this website has an image for the China Netcom line.
Using a unified domain name and then automatically guiding to different backup storages based on the user's line is the function of intelligent DNS (Intelligent DNS is actually part of CDN and the front-end part)

There are still some places where multiple domain names are used, such as downloading the image server from a website. Because intelligent DNS has some defects (it is not necessarily the right line, as described below ), it also provides users with the right to freely select lines.

At present, some companies also provide intelligent DNS interpretation services, pointing your domain name NS to their servers, and then entering the IP addresses of China Netcom and China Telecom servers.
Some companies also provide relatively complete CDN services, such as chinacache, which many medium-sized websites use.

The original bind does not support selecting different ip addresses from the source. Therefore, you can only use iptables to implement intelligent DNS. The method is also very simple. You can start two binds on the DNS server, do not use the default port. Resolve different lines in two copies, and then use iptables to send the DNS requests of the default port to different bind instances based on the source IP address.
The disadvantage of this method is obvious. Multiple bind instances are required. If more lines are needed, bind instances are required. In addition, iptables's interpretation of the source will also lead to too many iptables rules.

Currently, bind supports source selection. I am not sure whether it is a new feature of bind9. However, bind9 has been rewritten. Compared with bind8, it is much more stable and secure, the following configurations are based on bind9:

I am using CentOS, because the bind Service does not have other services (such as apache, squIdSo there is no need to compile a copy by yourself. I have used yum for installation, and the version is not the latest stable version.

After installation, you can use/etc/init. d/nam.EdStart starts the service
One file named. conf appears under/etc, which is the main config file of bind. We only need to modify it.
(I only describe the smart DNS implementation part, and modify other bind settings on your own)
Another tips: You can use/usr/sbin/named-g-u named to start bind. You can immediately see the output information for debugging convenience.

We use the view function of bind9 to separate and determine
First, we need a Netcom IP list, which is a list circulating on the Internet.

Acl "CNC "{
58.16.0.0/16;
58.17.0.0/17;
58.17.128.0/17;
58.18.0.0/16;
58.19.0.0/16;
58.255.0.0/16;
58.21.0.0/16;
58.22.0.0/15;
58.240.0.0/15;
58.242.0.0/15;
58.244.0.0/15;
58.246.0.0/15;
58.248.0.0/13;
60.0.0.0/13;
60.8.0.0/15;
60.10.0.0/16;
60.11.0.0/16;
60.12.0.0/16;
60.13.0.0/18;
60.13.128.0/17;
60.14.0.0/15;
60.16.0.0/13;
60.24.0.0/14;
60.30.0.0/16;
60.31.0.0/16;
60.208.0.0/13;
60.216.0.0/15;
60.218.0.0/15;
60.220.0.0/14;
61.48.0.0/13;
61.133.0.0/17;
61.134.96.0/19;
61.134.128.0/17;
61.135.0.0/16;
61.137.128.0/17;
61.138.0.0/17;
61.138.128.0/18;
61.139.128.0/18;
61.148.0.0/15;
61.156.0.0/16;
61.159.0.0/18;
61.161.0.0/18;
61.161.128.0/17;
61.162.0.0/16;
61.163.0.0/16;
61.167.0.0/16;
61.168.0.0/16;
61.176.0.0/16;
61.179.0.0/16;
61.181.0.0/16;
61.182.0.0/16;
61.189.0.0/17;
125.32.0.0/16;
125.40.0.0/13;
202.96.0.0/18;
202.96.64.0/21;
202.96.72.0/21;
202.97.128.0/18;
202.97.224.0/21;
202.97.240.0/20;
202.98.0.0/21;
202.98.8.0/21;
202.99.64.0/19;
202.99.96.0/21;
202.99.128.0/19;
202.99.160.0/21;
202.99.168.0/21;
202.99.176.0/20;
202.99.208.0/20;
202.99.224.0/21;
202.99.232.0/21;
202.99.240.0/20;
202.102.128.0/21;
202.102.224.0/21;
202.102.232.0/21;
202.106.0.0/16;
202.107.0.0/17;
202.108.0.0/16;
202.110.0.0/17;
202.111.128.0/18;
203.93.8.0/24;
203.93.192.0/18;
210.13.128.0/17;
210.14.160.0/19;
210.14.192.0/19;
210.15.32.0/19;
210.15.96.0/19;
210.15.128.0/18;
210.21.0.0/16;
210.52.128.0/17;
210.53.0.0/17;
210.53.128.0/17;
210.74.96.0/19;
210.74.128.0/19;
210.82.0.0/15;
218.8.0.0/14;
218.12.0.0/16;
218.21.128.0/17;
218.24.0.0/14;
218.56.0.0/14;
218.60.0.0/15;
218.67.128.0/17;
218.68.0.0/15;
218.104.0.0/14;
219.154.0.0/15;
219.156.0.0/15;
219.158.0.0/17;
219.158.128.0/17;
219.159.0.0/18;
220.252.0.0/16;
221.0.0.0/15;
221.2.0.0/16;
221.3.0.0/17;
221.3.128.0/17;
221.4.0.0/16;
221.5.0.0/17;
221.5.128.0/17;
221.6.0.0/16;
221.7.0.0/19;
221.7.32.0/19;
221.7.64.0/19;
221.7.96.0/19;
221.8.0.0/15;
221.10.0.0/16;
221.11.0.0/17;
221.11.128.0/18;
221.11.192.0/19;
221.12.0.0/17;
221.12.128.0/18;
221.13.0.0/18;
221.13.64.0/19;
221.13.96.0/19;
221.13.128.0/17;
221.14.0.0/15;
221.192.0.0/15;
221.194.0.0/16;
221.195.0.0/16;
221.196.0.0/15;
221.198.0.0/16;
221.199.0.0/19;
221.199.32.0/20;
221.199.128.0/18;
221.199.192.0/20;
221.200.0.0/14;
221.204.0.0/15;
221.206.0.0/16;
221.207.0.0/18;
221.207.64.0/18;
221.207.128.0/17;
221.208.0.0/14;
221.212.0.0/16;
221.213.0.0/16;
221.216.0.0/13;
222.128.0.0/14;
222.132.0.0/14;
222.136.0.0/13;
222.160.0.0/15;
222.162.0.0/16;
222.163.0.0/19;
222.163.32.0/19;
222.163.64.0/18;
222.163.128.0/17;
};

If you do not know which parts are accurate, you can modify them by yourself.