A very strange problem ~~~

A very strange problem ~~~ -- Linux Enterprise Application-Linux server application information. For details, refer to the following section. To solve the access speed problem of the company's website Telecom and Netcom users, we pulled two lines and set up a DNS server with bind9 for Intelligent Resolution. There is another local carrier, its
The IP address range is 221.136.0.0/16, 203.175.0.0/18, and 60.55.0.0/16. I add this segment to the Netcom CIDR block. However, when using these three lines to access the website, the Telecom IP address is given. After testing. when these three IP addresses are found in the LOG, a source IP address of 202.101.107.55 is given, instead of the IP address of 221.136.0.0 \ 203.175.0.0 \ 60.55.0.0, try to add 202.101.107.55 (a DNS of Quanzhou Telecom, Fujian province) to the China Netcom segment. After the test, it will be normal.
Although the problem has been solved, I still cannot understand its mysteries ~~~ Hope you will not hesitate to answer questions ~~~