In-a-Dyn :: DDNS�What and How

Joachim Wiberg

https://github.com/troglobit/inadyn

​

• DDNS = Dynamic DNS�Updated automatically
• DDNS Provider = ISP or Registrar�Usually an Internet Service Provider
• DNS Name for an IP Address�Most ISP customers have DHCP or PPPoE/PPPoA address today

What is it?

ISPs are everywhere, where their customers are. Many are also DDNS providers.��The client should support as many as possible, and support updating more than one DNS entry.

You need a DDNS client to actively track any change in your external IP address and then send an update to your DDNS provider(s)

• Check IP�Most DDNS providers have a server�http://checkip.dyndns.com/
• Update DNS Entry�Can be done manually, of course, but most users prefer an automatic service do this for them

How to use it?

Common Use-case

User has multiple connected sites Each site has a DHCP address

How do we set up a VPN to each site when ISPs can change address at any time?

Solution: DDNS

Sites connect to DDNS provider to keep their DNS entry up-to-date

VPN can be initiated from either end�Usually on-demand service VPNs are used. Works with Roadwarriors too

Protocol

But wait, what about HTTP POST to update?

Cloudflare, Yandex, DNSPod

Use HTTP GET to get IP address and HTTP GET to update the DNS

Dyn.com

Oh Dyn.com get a lot of customers

Let’s copy them!

Every other provider, e.g. Loopia, D.U.I.A., FreeDNS

Sounds simple, let’s wrap curl in a shell script!

Well … scripts work for many use-cases but there are things the DDNS providers don’t want you to know:

• Too frequent updates = block�Many DDNS providers implement an automatic block if you send updates (without actual IP change) “too often”
• Connectivity/Provider issues�No Internet, we’ve all been there, but now the provider doesn’t respond or�responds weirdly?

Problems

Testing

HTTPS certificates, IPv4 vs IPv6, DDNS providers that block too frequent updates, etc.

How to test this?

You guessed it, manually …

​

Questions?

​

​

​

​

​

​