how to tell the dns to cache the domain name when request the same host machine frequently?

[doEveryday]

I need send a request to more than 40 machines by domain name ,and each
time maybe give different url (e.g
www.ret.com/getdata.htm,www.ret.com/updatedata.htm....) ,I know that
the dns server will convert the domain name(www.ret.com) to IP
address,I think that each time the dns need to do so work, it wastes so
much time, if I can set any parameter to tell dns server to cache the
domain name, After the first request, it will no more do converting
action.
 could someone tell me which module can do so work?