0

I am currently building a tool that needs the response from multiple different DNS Servers. The programming part is all done but I am currently lacking the IP Addresses of major ISP DNS Servers. All I can find are, what I assume, old ones that don't work anymore. When entering my local DNS Server or Public DNS Servers (Google, Cloudflare, etc.) I get the expected result. So my question is, is there a list or way to find the DNS Servers from those ISPs? (Specifically, ISPs located in Germany)

Techguy59911
  • 3
  • 1
  • 3
    You appear to assume that the same IP provided for the ISP customers will a) respond to you, a non-customer and b) respond in a similar fashion to you as it does to queries from inside their networks. Consider clarifying the end goal instead of just the possible solution you are thinking of now. – anx Jan 12 '22 at 00:35
  • Are you interested in standards compliance / DNSSEC bugs? Or internet censorship? Or just trying to verify some cache will expire? There are existing tools for all of that.. – anx Jan 12 '22 at 00:38
  • 2
    "So my question is, is there a list or way to find the DNS Servers from those ISPs?" Not in any automated exhaustive way. There are no reasons for ISPs to publicly give this information, and even if they do their nameservers should probably not reply for queries from outside of their network. – Patrick Mevzek Jan 12 '22 at 04:14
  • @anx My tool is intended to automatically check wether a DNS block is currently in place or not and if so what ISPs are doing it since I don't want to rely on only a single ISP. As far as I know there is no such tool for the specific use case. There is a website where you can enter the url and the owner of that site checks it manually. – Techguy59911 Jan 12 '22 at 07:27

1 Answers1

2

Since public DNS resolvers can be used in for example DNS amplification DDoS attacks most properly managed ISP's and networks limit access to their resolvers. They will have firewalls and other security mechanisms to ensure exclusive access to their own networks & customers.
And you won't be able to query them remotely.

Additionally I think that ISP's prefer to assign DNS & other settings via DHCP to keep them dynamic to allow them to easily make changes in their infrastructure. They will avoid publishing their DNS server IP's to prevent customers from making static network configurations that will break when the ISP makes changes.

Those two combined make your quest futile, I think.

Bob
  • 5,805
  • 7
  • 25
  • So the only solution I could think of would be to have multiple servers each one with a different ISP, right? – Techguy59911 Jan 12 '22 at 08:21
  • Indeed, you would need to run your checks from a system inside the network of that particular ISP. – Bob Jan 12 '22 at 08:27