DNS Not Working? Fix Common DNS Errors — Troubleshooting Guide

dig (Domain Information Groper)

The most powerful DNS diagnostic tool on the command line:

# Basic query
dig example.com A

# Query specific DNS server
dig @8.8.8.8 example.com A

# Short output
dig +short example.com A

# Full trace (entire resolution path)
dig +trace example.com A

# With DNSSEC info
dig +dnssec example.com A

# Reverse lookup
dig -x 93.184.216.34

nslookup

# Basic query
nslookup example.com

# Choose record type
nslookup -type=mx example.com

# Query specific server
nslookup example.com 8.8.8.8

host

# Simple query
host example.com

# Specific record type
host -t mx example.com

Problem: "DNS_PROBE_FINISHED_NXDOMAIN"

Meaning: The domain does not exist in DNS.

Possible causes:

• Domain has expired → Check registrar, renew domain
• Nameservers not configured → Set NS records at registrar
• Typo in domain → Check URL
• DNS propagation not complete → Wait and check again

Problem: Emails Not Being Delivered

DNS Checklist:

1. MX records correct? → dig example.com MX
2. MX target has A record? → dig mail.example.com A
3. Reverse DNS (PTR) correct? → dig -x [IP]
4. SPF record present? → dig example.com TXT | grep spf
5. DKIM record present? → dig selector._domainkey.example.com TXT
6. DMARC record present? → dig _dmarc.example.com TXT

Problem: Website Shows Old Content After Server Switch

Cause: A record still points to old server (caching).

Solution:

1. Check authoritative NS: dig @ns1.example.com example.com A — does it show the new value?
2. Clear local cache
3. Test different global resolvers (8.8.8.8, 1.1.1.1, 9.9.9.9)
4. Wait until the TTL has expired

Problem: SERVFAIL Response

Possible causes:

• DNSSEC validation failed → Check DS record and signatures
• Authoritative nameserver unreachable → Check nameserver health
• Misconfigured zone → Check zone file for syntax errors

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