设计一个DNS服务器程序，读入“域名-IP地址”对照表，当客户端查询域名对应的IP地址时，用域名检索该对照表，三种检索结果：

检索结果为ip地址0.0.0.0，则向客户端返回“域名不存在”的报错消息（不良网站拦截功能）

检索结果为普通IP地址，则向客户返回这个地址（服务器功能）

表中未检到该域名，则向因特网DNS服务器发出查询，并将结果返给客户端（中继功能）

考虑多个计算机上的客户端会同时查询，需要进行消息ID的转换

-Designing a DNS server program, reads "domain name-IP address" table, when the client queries the domain name corresponds to the IP address, domain name to retrieve a table, three types of search results:

Search results for IP address 0.0.0.0, then returned to the client "domain does not exist" error (bad website blocking)

Retrieve the results as a normal IP address, this address is returned to the client (server functionality)

Did not pick up the domain name in the table, is sent to the Internet DNS Server query, and return the result to the client (relay)

Consider the client to query on multiple machines, you need to convert message ID