1.1.1.1 suddenly stopped working as DNS for our network

We were using Cloudflare’s 1.1.1.1 as our DNS servers for our network and everything has been working fine for months. This morning we came in to work and the network could not reach any domain names (amazon.com, google.com, etc…). Our camera system & voip phones were working since they use a static IP.

We tracked the issue down to Cloudflare’s DNS not being reachable by the network, so it wasn’t resolving any domains.

I changed the DNS servers to use Google’s 8.8.8.8 and everything started working fine.

Why might this have happened? Where we blocked by Cloudflare and if so, how to do we confirm that and appeal it.

Thanks!

It’s extremely unlikely Cloudflare is blocking your access to 1.1.1.1. More than likely, it’s something in your network path that’s blocking it.

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I thought the same. Our ISP, which is the University campus we’re on, swears they aren’t blocking it, and our internal network is not either (I can directly confirm that).

If you are curious, you can perform a traceroute and then a mtr, with mtr specified udp, as some routers block traceroute icmp echo or limit it. It should be able to give you some hints but you may or may not be able to solve it.

https://www.cloudflare.com/learning/network-layer/what-is-mtr/

That’s why the instructions I posted told you to do a traceroute.