Command Reference

Replace example names and documentation addresses before using these commands.

Registration and Delegation

dig NS example.dpdns.org
dig +trace NS example.dpdns.org
dig SOA example.dpdns.org

Direct Authoritative Queries

dig @ns1.dns-service.example SOA example.dpdns.org
dig @ns1.dns-service.example A example.dpdns.org
dig +tcp @ns1.dns-service.example SOA example.dpdns.org

Website Records

dig A example.dpdns.org
dig AAAA example.dpdns.org
dig CNAME www.example.dpdns.org
dig CAA example.dpdns.org

Email Records

dig MX example.dpdns.org
dig TXT example.dpdns.org
dig TXT selector1._domainkey.example.dpdns.org
dig TXT _dmarc.example.dpdns.org

Short Answers

dig +short A example.dpdns.org
dig +short NS example.dpdns.org

Short output is convenient for scripts but removes useful flags, authority, and TTL context. Use normal output during diagnosis.

HTTP and Redirects

curl -I http://example.dpdns.org
curl -I https://example.dpdns.org
curl -L -o /dev/null -s -w '%{http_code} %{url_effective}\n' http://www.example.dpdns.org

Test a Virtual Host Before DNS

curl -I -H 'Host: example.dpdns.org' http://192.0.2.10
curl --resolve example.dpdns.org:443:192.0.2.10 -I https://example.dpdns.org

The HTTPS command validates the certificate for the hostname while connecting to the selected address.

TLS Certificate

openssl s_client -connect example.dpdns.org:443 -servername example.dpdns.org </dev/null

Summarize certificate fields:

openssl s_client -connect example.dpdns.org:443 -servername example.dpdns.org </dev/null 2>/dev/null \
  | openssl x509 -noout -subject -issuer -dates -ext subjectAltName

Local Listening Ports

Linux:

sudo ss -lntup

macOS:

lsof -nP -iTCP -sTCP:LISTEN

Web Server Checks

sudo nginx -t
systemctl status nginx --no-pager
journalctl -u nginx --since '30 minutes ago' --no-pager

Connectivity

nc -vz example.dpdns.org 80
nc -vz example.dpdns.org 443

A successful TCP connection does not prove that HTTP, TLS, or the application is correct.

Save Diagnostic Output

{
  date -u
  dig NS example.dpdns.org
  dig A example.dpdns.org
  curl -I --max-time 15 https://example.dpdns.org
} > domain-diagnostic.txt 2>&1

Review the file and remove personal data, internal hostnames, tokens, cookies, and unrelated output before sharing it.

Continue to Website Architecture Patterns.