DNS is broken. Network is fine. What do you check first?

You can ping 8.8.8.8, but google.com won't resolve.

Now imagine the same thing happening inside Kubernetes – pods can reach IPs, but service names suddenly stop resolving.

What do you check first: CoreDNS, /etc/resolv.conf, network policy, or the upstream DNS server – and what evidence would you look for before changing anything?