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I recently opened a dynamic dns user (at no-ip for that matter..) for my own personal needs and especially for ssh-ing my computer whenever I need to, without knowing it's static IP.

My questions are:

  • Am I misusing the concept of dynamic dns? Are there more appropriate methods to do what I want to do?

  • If not, how do I resolve my router's real ip address? Firefox somehow manages to do so, nslookup and other similar commands only resolve the ip of the ddns server (e.g. no-ip.org). Trying to figure this mystery with wireshark failed miserably ;)

Bart De Vos
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stnr
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    Have you ever read the documentation before asking? http://www.no-ip.com/support/faq/EN/dynamic_ddns/ – mailq Nov 27 '11 at 12:13
  • Yes. Found answer (sort of) to my first question. The second one is still open. – stnr Nov 27 '11 at 12:22

4 Answers4

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I use another service : dyn dns but the operations are similar.

For free they gave you a record in their dns servers, under one of their domains. I choose saltlake.dyndns.org

I have a adsl, at connection and also at random times, I get a new ip address. There are many web sites to check your external, public ip address, e.g. www.whatsmyip.org

If I ping my dns record saltlake.dyndns.org I get my current public ip, right.

How does it work ? Simple : you have to run a little agent, it contacts the dyndns servers when the ip change, or every few minutes. They receive this packet, see your new public ip address, they update your dns record.

The agent can be your router ( many adsl routers support dyndns and similars services ), or you have to run a little agent on your operating system.

About dns propagation times, it is far better than 10 years ago. I just disconnet my adsl line, reconnect, check with whatsmyip.org my ip address ( its different ) and ping saltlake.dyndns.org : I get the new ip. A few seconds - and it verifies the agent is doing its job.

Ah, for the sake of completeness. When you ping you free record, ping uses dns to find the current ip ... and apply a reverse query to find the real name associated to the ip.

For example, with my adsl home line ping saltlake.dyndns.org shows my external ip and also dynamic-adsl-62-10-39-166.clienti.tiscali.it ... wow, two dns records, I am a VIP !

About the slow times, imho they are not due to the dns tree update or the cheapo adsl lines. It is the excuse by some free dns providers, not working so well.

Massimo
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Since your address works in web browser and not in nslookup, you probably set-up "web redirect" instead of "A" record.

Web redirect adds an "A" record pointing to provider server and that server forwards incoming requests to your IP using port forwarding or HTTP redirection.

You do not misuse concept of dynamic DNS, it intended just for this purpose (providing you capable of opening ports that you need in your router and firewall).

Sandman4
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DDNS are useful when you have a connection with a dynamic ip address(a new ip address is assigned by ISP at every connection attempt) and you want to access from external place some services behind that connection.

You can find the IP address of your router connection simply pinging that DNS name, so for example : 

> ping yourdns.no-ip.org

in the response you will get the public ip address of your router.

aleroot
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The main purpose of dynamic DNS services is to enable systems without an external static IP address to be "easily" accessed from remote networks (sometimes referred to as the Internet) via a domain name.

The dynamic DNS client application communicates on short intervals with your dynamic DNS provider, and when your external ip address changes, your dynamic DNS provider's DNS records change accordingly.

If you're using a dynamic DNS service to access your system from an external network, then no, you are not misusing the concept of dynamic DNS.

You can resolve your external IP address either by pinging the domain name that your dynamic DNS provider gave you or by querying your domain name in nslookup or dig.

Keep in mind that DNS records need some time to propagate. Don't expect to signup for a dynamic DNS account and be able to resolve your external address via the domain name provided right away. It might take some time.

dkaragasidis
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  • As reading my question will tell you, firefox (and any other browser) somehow manages to resolve the real ip address. So it has been already updated. – stnr Nov 27 '11 at 12:41
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    Well, Firefox does not "resolve" domain names. Neither does ping, traceroute or any other application that can handle domain names. It is a task handled by the operating system. Have you modified /etc/hosts file or have a local DNS server? – dkaragasidis Nov 27 '11 at 12:48
  • Well, their results are still different, so something is still done differently here, the terminology is not so interesting to me. – stnr Nov 27 '11 at 12:59