Troubleshooting coredns

Kubernetes version: v1.26.2
Cloud being used: bare-metal
Installation method: kubeadm
CNI Flannel latest
CRI docker with Mirantis cri-dockerd as Docker Engine shim
K8s node is Host Ubuntu 22.04
My host can nslookup to a public IP address
I create a dnsutils pod and try nslookup with it

root@dnsutils:/# nslookup

** server can't find NXDOMAIN

But it can resolve other domain normally


Non-authoritative answer:

How can I troubleshoot it ?
I cannot get certificate from cert-manager because my challenges complain that it cannot resolve to IP address

kubectl challenges -o wide
NAME                                              STATE     DOMAIN                     REASON                                                                                                                                                                                                                                                                                                                                                                                 AGE
app-tls-jv6lp-4092342631-2629679118   pending   Waiting for HTTP-01 challenge propagation: failed to perform self check GET request '': Get "": dial tcp: lookup on no such host   3m58s

Please give me some advice, thank you very much.

The problem relating to network setting , I fixed it, thank you very much