Alhvi Balcarcel's List: Networking

Hi Rhys, you do not need to add any entry to the DNS manager. I will explain why:
Basically, each domain has some settings that say which Name Servers (NS) control it. When other Name Servers or People try to look up the address of the server (i.e., domain.com), then query the nameservers for domain.com, and they will respond with an IP address. If you have a subdomain, because this is still part of domain.com, all information about domain.com will reside in the specific nameservers for it. I.e., subdomain.domain.com, reallybigcarrots.domain.com, and domain.com will all have their settings on the same nameservers (i.e., NS1.DNSHOST.com, NS2.DNSHOST.com, etc). These settings can point to any IP address you like, however, you cannot have a subdomain controlled by a different nameserver (and there's no point to it). This is why you do not have to add it to Linode's DNS manager - this is only for domains that are controlled by Linode's Name Servers. As this is a subdomain, adding it in Linode's DNS manager will be pointless, because no one will look there for the information.

This is also not needed, because your web server will respond either based on people requesting the IP address (a dedicated host/website), or, based on the domain/subdomain being requested (for shared/VHOST'd sites). I.e., if I pointed a subdomain of my site (for example, rhys.greyhat-security.com) to your Linode's IP, I'd either get
a) Your website displaying (in the case of 1 dedicated website for that IP address)
or
b) A blank/default page, until you tell your web server that rhys.greyhat-security.com points to such-and-such a sub-folder