Subdomains and security with regards to root domain

[supercut]

Hi:
I'm hoping to get a confirmation from the security gurus that my thinking is correct. I'm looking to set up a subdomain such as test.mydomain.com from my main domain (mydomain.com) using a A record in the DNS. So the subdomain will in fact be hosted on a different server. The reason for this is because I'll be putting up some PHP scripts that have not been thoroughly tested yet for security, so in case the PHP scripts are exploited, the hacker can atmost only affect the subdomain.

Is my thinking correct on this as far as full isolation between the subdomain and main domain as far as security when the former is hosted on a separate server using A record? I mean, the two domains should basically be on two separate servers in every since of the word.

Thanks,

[swemic]

I'm not 100% sure on what exactly you asking here, but you certanly don't need to have a sub-domain to secure a test server. However, in some certain environments it can be pretty neet to separate the main-domain by a sub-domain.
Anyhow, you should be just fine by adding a separate A record for another server which is not on the same sub-net or server as your other servers are located.
If you yet wish to have a subdomain, it will allways be your NS that is responsible for your "top" domain, which in this case is your complete domain.
NS example.com
Will act as a root-dns for everything from hereafter to example.com
even if you wish to have an sub-domain like test.example.com, this domain has to be defined in some what also at your NS, but that can be just as simple as a entry in your /etc/named.conf stating the server is located on another IP

[adam7979]

depends....

what do you want to do with test.domain .com btw?

visitors -> http://www. domain .com, and they will be routed to test.domain .com ? or you're the only one using test.domain .com?