Why does apache fail to execute access restrictions based on the host name or domain name?

Article Title: Why does the access restriction of apache based on host name or domain name fail to be correctly executed. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.
Problem Analysis: There may be two reasons: first, there is a problem with the data on the DNS. for example, you have imposed access restrictions on foobar.example.com, but in fact foobar.example.com is only an alias for other domain names, in this way, when foobar.example.com accesses you, Apache returns a real domain name through address-domain name lookup, instead of foobar.example.com, so access restrictions are correctly executed. The second is that the test in Apache configuration is insufficient.
Solution: in the first case, you must find the real domain name of foobar.example.com to restrict access to it. in the second case, you can add the EXTRA_CFLAGS =-DMAXIMUM_DNS parameter during compilation, however, this will cause frequent DNS searches, resulting in lower performance.