Path MTU discovery troubleshooting
Find PMTU drop hop; ping -M do forbids frag to pinpoint blackhole MTU
tracepath -n <host>; ping -M do -s 1472 -c2 <host>
more troubleshooting
all 32 commands →
Confirm egress route and ARP
ip route get <ip>; ip neigh show | grep -E 'FAILED|INCOMPLETE'
TCP port reachability past firewall
traceroute -T -p 443 <host>; nc -zv <host> 443
Bypass DNS with curl --resolve
curl -sv --resolve <host>:443:<ip> https://<host>/healthz
In-cluster DNS smoke test
kubectl run dnsutils --image=tutum/dnsutils -it --rm --restart=Never -- nslookup kubernetes.default
Query CoreDNS directly
dig +short @$(kubectl -n kube-system get svc kube-dns -o jsonpath='{.spec.clusterIP}') <name>.<ns>.svc.cluster.local