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What is DDNS (Dynamic Domain Name System) and how to use it?
What is DNS?
DNS service (Domain Name System) is used for the conversion of IP addresses from domain name to the numeric format. This means that there is no need to keep in mind the address, but it is sufficient to remember www.dipol.com.pl. Translation of the domain name into the set of numbers is performed by the appropriate DNS server, to which the computer sends a query asking for the translation of the address. After receiving the response with the numeric address, the computer connects to the appropriate computer/server.
Diagram of client - server communication:
1. Which is IP address equivalent to www.dipol.com.pl ?
2. www.dipol.com.pl is
3. Hi, ! Send me your www content.
4. Here it is!
Such communication is possible when the destination server has a static IP address at which it is always accessible. The record, once placed in the database, linking the address with www.dipol.com.pl, is always up to date and constant. Therefore, the client can communicate with the server either by its domain address (using the DNS translation) or directly by the numerical address (without help of DNS service).
What is DDNS?
If we wish to run a server for website hosting or accessing CCTV camera, available from any Internet location and we don't have a static IP address but a dynamic one supplied by DHCP server (Neostrada - ADSL service in Poland is a good example of such an option), we have to use DDNS (Dynamic Domain Name System) service.
How does DDNS work?
Neostrada clients do not have a static IP - it is changed periodically. As we have shown above, in this situation it is impossible to run a server, because the current IP address of the server would have been unknown. DNS server, which translates domain name into numeric form, points at one specific IP. Once the IP number changes, the DNS data ceases to be valid.
The solution is provided by DDNS service. Similarly to DNS server, it provides a database containing relations between domain and numeric addresses, but this database may be updated on request by the domain owner. Thanks to this feature, the server is available in the domain address regardless its actual IP number. In such a case, the access to the server is limited to its domain name translated by DDNS server, unless we know its actual IP number (but of course we do not know how long it will be valid).
We have to remember that when DHCP server changes the IP, it takes some time to detect this change by the client software or router, and, after the notification is sent to DDNS server, it takes another minute or so to send this piece of data to DNS server to update the database. In result, our server will be periodically unavailable up to several minutes, every time the IP address has been changed.
DDNS in action:
1. Your IP address is
2. dipol.no-ip.org to is
3. What is current IP address of dipol.no-ip.org?
4. dipol.no-ip.org is now
5. Hi, send me your www content
6. Here it is!
7. Your IP address has changed to
8. dipol.no-ip.org is now
9. What is the current IP of dipol.no-ip.org?
10. dipol.no-ip.org is now
11. Hi, Send me your www content.
12. Here it is!
DDNS service is accessible via a number of providers. Its basic version, sufficient to support the above configuration, is usually free of charge. All devices supporting DDNS usually have several provider addresses preset by default. The most popular are:
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