Can multiple dynamic DNS resolve to the same IP address? I would like to keep some things separate in my home network and wondered if I can use different dynamic DNS addresses to resolve to my home IP?
Can multiple dynamic DNS [addresses] resolve to the same IP address?
I would like to keep some things separate in my home network and wondered if I can use different dynamic DNS addresses to resolve to my home IP?
You can certainly do this, but as suggested by w3dk you will need to differentiate the traffic somehow on your home network. The simplest way to do this is by also using separate ports for each service. If you have some "services" that somehow operate only on one port (e.g. a web server serving two or more separate http:// sites) then you will need to look in to a method of separating out that traffic in another manner (e.g. virtual hosts).
Dynamic DNS services update the "A record" for your domain, which can point to any IP address. So you can have any number of domains, dynamic or not, pointing to the same IP.
But you can also create aliases for a domain. Those are called "CNAME records". That way you would only need to setup a single dynamic IP domain, and as many aliases as you want, which will always resolve to the dynamic IP. You can create those in any domain registrar, sometimes hidden as "Adanced DNS" or such.
FreeDNS lets you create free subdomains in other people's domains—and also share your own if you so wish. It also provides dynamic IP updating—though not many routers support it—, so it's great for home/test servers and what not. I have a subdomain pointing its "MX record" (that's for email) to mailinator.com, for example, to register in annoying sites that block Mailinator's own aliases (CNAMEs).
As for "keeping things separate", that's going to be though by just using different domains. Most services don't bother checking for anything but that the port they listen to receives something. OpenVPN would give the same answer in every domain that points to your IP (and in the raw IP too, of course). Web servers can answer in different ways according to the domain used to reach them, so you can have several websites in the same server (even thousands of them, like all the friendly $5 Shared Webhosts, which like to live in the edge ;), but they will present a website (or at least an error page) in every domain that points to your IP.
You would probably be better off restricting who can connect to what, like, restricting—in your firewall—your OpenVPN port to only answer to a certain IP; at least with iptables, you could specify a dynamic domain instead of an IP, but iptables would resolve its address while starting up, so it would stop working as soon as the address changes, so you would have to reload iptables regularly to avoid downtime. Or perhaps you only want a cosmetic separation, and don't care if a snooper finds your open ports in either domain. But I'm just playing psychic by now; you should provide plenty more details of what is what you want and why, to get better help.