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What is DDNS

Posted on 2006-11-25
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What is the advantage of DDNS and is it easy to use. How is the domain name is organize. Please give mesome detail brief on this type of network
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Question by:kianhow
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Juan Ocasio earned 500 total points
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DDNS or DYnamic DNS is a service that allows you to map a dynamic external IP address with a friendly name as in abc.gotdns.com.  If you go to dyndns.com, you'll get alot of information on this.  As static IP addresses are more expensive that dynamic ones this service is pretty decent.  I use it to allow me to get to my FTP server when I'm not at home.  Basically the way it works is you have an external IP address given to you by your ISP.  This is usually dynamic meaning it could change.  When you sign up for DDNS, you're mapping your current external IP address with a specific name.  THe caveat to this is you do not have a choice on the domain name.  For example, with DynDNS, you have to select one of their domain names (like gotdns.org, homeunix.org, etc).  The first part of the name can be anything (myName.gotdns.com, for example), but if you have a business, this probably won't be the best solution.

Once you map the name to the ip address, you have a client service installed on your machine (a lot of new routers actually have this installed now) and it checks periodically and remaps your external ip address to your domain name.  That way you can just type in your domain name and you'll alway point to your external IP address.

HTH

jocasio
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by:jeffkell
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There are several meanings to "Dynamic DNS" - I'm not certain which one you are asking about, so I'll review them briefly.

DNS obviously translates a domain name (computer.company.com) into an IP address (1.2.3.4), and reverse DNS does the opposite function, translating the IP address back to a name, using the "in-addr.arpa" namespace (e.g., 4.3.2.1.in-addr-arpa => computer.company.com).  As long as your IP never changes, this works rather well with static DNS tables that remain fixed.

Dynamic DNS tries to address issues where the IP address of a computer is not fixed.  If your computer gets it's IP address dynamically, such as via DHCP, it may not receive the same IP address every time the DHCP lease is obtained or renewed.  In a typical Windows server environment, the DHCP and DNS services are integrated on the server and combine to provide DDNS.  When a computer obtains an IP address, the DNS tables are updated with the computer name pointing to the newly assigned IP address.  When the lease expires, the DNS entry is removed.  This isn't just a Windows thing anymore, ISC's bind and dhcpd can provide DDNS as well.

This is relatively easy to do within an organization, and since the organization controls the names, IP addresses, and DNS/DHCP services, DDNS can be used to provide both forward and reverse DNS for the clients of the DHCP server.  

The other type of dynamic DNS such as jocasio123 mentions is more common when you do not control the domain name, IP address, DNS, and/or DHCP service.  If you want to have your own web server, for example "www.myname.com", without having all of the underlying IP/DNS/DHCP control, there are several providers that can provide a form of "dynamic" DNS for you.  In the example above, you can't pick your own full domain name, just the hostname part.  You would get a hostname from the DDNS provider and end up with a server name like "www.myname.ddns-provider.com".  Whenever your computer starts up and gets an IP from whatever source (typically your ISP's DHCP service), your computer then "registers" with your DDNS provider to link your current IP address with the name you registered.  The advantage here is that you only need to do business with the DDNS provider for the name.

You can also get a "complete" name from other providers.  Here, you register your own "myname.com" domain name with one of the various domain registries, then register this name with one of the DDNS providers.  When you register "myname.com" you specify the DDNS provider's DNS servers in your registration, so that lookups for "myname.com" use the DDNS provider.  Your computer registers it's IP address after getting a DHCP lease the same as above, but now you have a full name (www.myname.com) instead of just a hostname (www.myname.ddns-provider.com).  To get this full name, you must now do business with your internet registry provider (to keep the myname.com registered) AND your DDNS provider (to keep the DNS service active).

Note that in both cases that you will typically NOT get reverse DNS, since your ISP still controls your IP namespace (and delegation of the in-addr.arpa section of your IP address).
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