Point one subdomain to another

Hello,
I am having one subdomain m.example.com?site=abcd which I want to point to m.abcd.com . So whenever user will goto m.abcd.com it will open m.example.com?site=abcd with m.abcd.com will remain in the addressbar. Is it possible to do this? Please help me. Thanks in advance.

Are both sites on the same server?

No both are on different server.

If you configure m.abcd.com so that it resolves to the same server as m.example.com (using either an A record or a CNAME record) you could then configure your application on m.example.com to serve the same content as m.example.com?site=abcd. The way you configure this would not be DNS-related (it would be specific to whatever software the server is running).

If you can't configure m.abcd.com so that it resolves to the same server as m.example.com or if you can't configure m.example.com to serve requests for m.abcd.com, you could instead set up a proxy server on m.abcd.com that forwards requests to m.example.com?site=abcd. This also would not be done using DNS. If you use the Apache web server you can do it using mod_proxy.

Not quite sure but as a guess (if your are using asp.net) then you can use Request.Transfer to serve the contents from different source without actually changing the url in address bar.