Troubleshoot DNS Resolution Skill

Systematic diagnosis and resolution of DNS resolution issues in the Pi-hole DNS infrastructure.

Quick Start

Run quick diagnostic to identify DNS issues:

# Check DNS resolution
dig @192.168.68.136 pihole.temet.ai

# Check Pi-hole is running
docker ps | grep pihole

# Check DNS records configured
docker exec pihole nslookup pihole.temet.ai 127.0.0.1

Table of Contents

1. When to Use This Skill
2. What This Skill Does
3. Instructions
   • 3.1 Verify Pi-hole is Running
   • 3.2 Check Pi-hole DNS Configuration
   • 3.3 Test DNS Resolution from Pi-hole
   • 3.4 Verify Router DNS Settings
   • 3.5 Test DNS Resolution from Client
   • 3.6 Check FTLCONF DNS Records
   • 3.7 Apply Fix
4. Supporting Files
5. Expected Outcomes
6. Requirements
7. Red Flags to Avoid

When to Use This Skill

Explicit Triggers:

• "DNS not working"
• "Can't access pihole.temet.ai"
• "Domain not resolving"
• "Fix DNS resolution"
• "Pi-hole DNS not working"

Implicit Triggers:

• Services work via IP but not domain name
• Browser shows "DNS_PROBE_FINISHED_NXDOMAIN"
• Can access services remotely but not locally
• Ping fails for local domains

Debugging Triggers:

• "Why isn't my domain resolving?"
• "Why can't I access local services?"
• "Is Pi-hole working?"

What This Skill Does

1. Verifies Pi-hole - Checks Pi-hole container is running
2. Checks DNS Config - Verifies FTLCONF DNS records in docker-compose.yml
3. Tests Pi-hole DNS - Queries Pi-hole directly for DNS records
4. Checks Router - Verifies router is configured to use Pi-hole
5. Tests Client DNS - Verifies client devices can resolve domains
6. Identifies Issue - Determines root cause of DNS failure
7. Provides Fix - Gives specific commands to resolve the issue

Instructions

3.1 Verify Pi-hole is Running

docker ps | grep pihole

Expected: Container status "Up" (not "Restarting" or "Exited")

If not running:

cd /home/dawiddutoit/projects/network && \
docker compose up -d pihole && \
docker logs pihole --tail 50

3.2 Check Pi-hole DNS Configuration

Verify FTLCONF_dns_hosts environment variable is set:

docker exec pihole env | grep FTLCONF_dns_hosts

Expected output should include:

FTLCONF_dns_hosts=192.168.68.136 pihole.temet.ai
192.168.68.136 ha.temet.ai
192.168.68.136 jaeger.temet.ai
...

If missing or incorrect: Edit docker-compose.yml to add/update FTLCONF_dns_hosts environment variable.

3.3 Test DNS Resolution from Pi-hole

Test that Pi-hole itself can resolve the domain:

# Test single domain
docker exec pihole nslookup pihole.temet.ai 127.0.0.1

# Test all configured domains
for domain in pihole ha jaeger langfuse sprinkler code webhook; do
  echo "=== Testing $domain.temet.ai ==="
  docker exec pihole nslookup $domain.temet.ai 127.0.0.1
  echo
done

Expected: Shows "Address: 192.168.68.136" for each domain

If "NXDOMAIN" or "can't find":

• DNS records not configured in FTLCONF_dns_hosts
• Pi-hole FTL hasn't loaded the configuration

Fix:

# Reload Pi-hole DNS
docker exec pihole pihole reloaddns

# Or restart Pi-hole
docker compose -f /home/dawiddutoit/projects/network/docker-compose.yml restart pihole

3.4 Verify Router DNS Settings

Check router is configured to use Pi-hole as DNS server:

Router should point to: 192.168.68.136 (Pi-hole IP)

How to verify:

1. Log into router admin interface
2. Check DHCP settings
3. Verify DNS server is set to 192.168.68.136

Common router interfaces:

• Eero: App → Settings → Network Settings → DNS
• Unifi: Network → Settings → Networks → LAN → DHCP Name Server
• Generic: Usually under LAN/DHCP settings

3.5 Test DNS Resolution from Client

From your computer or device:

# Check what DNS server you're using
scutil --dns | grep "nameserver\[0\]"

# Test resolution using system DNS
dig pihole.temet.ai

# Test resolution using Pi-hole directly
dig @192.168.68.136 pihole.temet.ai

Expected:

• System DNS should show 192.168.68.136
• Both dig commands should return 192.168.68.136 as answer

If using wrong DNS server:

• Client may have cached old DNS settings
• Router may not have updated DHCP lease
• Client may have manual DNS override

Fix:

# Flush DNS cache (macOS)
sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder

# Renew DHCP lease (macOS)
sudo ipconfig set en0 DHCP

# Linux
sudo systemd-resolve --flush-caches

3.6 Check FTLCONF DNS Records

Verify DNS records are configured in docker-compose.yml:

grep -A20 "FTLCONF_dns_hosts" /home/dawiddutoit/projects/network/docker-compose.yml

Expected format:

FTLCONF_dns_hosts: |
  192.168.68.136 pihole.temet.ai
  192.168.68.136 ha.temet.ai
  192.168.68.136 jaeger.temet.ai
  192.168.68.136 langfuse.temet.ai
  192.168.68.136 sprinkler.temet.ai
  192.168.68.136 code.temet.ai
  192.168.68.136 webhook.temet.ai

If missing domains: Add them to FTLCONF_dns_hosts and restart Pi-hole.

3.7 Apply Fix

Fix A: Pi-hole Not Running

cd /home/dawiddutoit/projects/network && \
docker compose up -d pihole && \
docker logs pihole --tail 50

Fix B: DNS Records Not Configured

1. Edit docker-compose.yml:

nano /home/dawiddutoit/projects/network/docker-compose.yml

2. Add missing domains to FTLCONF_dns_hosts:

FTLCONF_dns_hosts: |
  192.168.68.136 newservice.temet.ai

3. Restart Pi-hole:

docker compose -f /home/dawiddutoit/projects/network/docker-compose.yml up -d pihole

Fix C: Client Using Wrong DNS

1. Check router DHCP settings point to 192.168.68.136
2. Renew client DHCP lease
3. Flush client DNS cache

Fix D: Pi-hole DNS Not Reloaded

# Reload DNS without restart
docker exec pihole pihole reloaddns

# Or full restart
docker compose -f /home/dawiddutoit/projects/network/docker-compose.yml restart pihole

Supporting Files

Expected Outcomes

Success:

• Pi-hole container running and healthy
• DNS queries to Pi-hole return correct IP addresses
• Client devices resolve domains correctly
• All configured domains accessible via domain name

Partial Success:

• Pi-hole resolves correctly but clients still using old DNS
• Records configured but not yet propagated to clients

Failure Indicators:

• Pi-hole container not running
• FTLCONF_dns_hosts missing or incorrect
• Router not configured to use Pi-hole
• DNS resolution returns NXDOMAIN

Requirements

• Docker running with Pi-hole container
• Pi-hole v6+ using FTL DNS server
• Network access to Pi-hole (192.168.68.136)
• Router admin access to configure DHCP/DNS

Red Flags to Avoid

• Do not use dnsmasq configuration files (Pi-hole v6 uses FTL with FTLCONF variables)
• Do not add DNS records via Pi-hole web UI (use FTLCONF_dns_hosts instead)
• Do not forget to restart Pi-hole after changing FTLCONF_dns_hosts
• Do not configure DNS manually on clients (use router DHCP instead)
• Do not skip flushing DNS cache on clients after DNS changes
• Do not use -uall flag with Pi-hole DNS queries (causes memory issues)

Notes

• Pi-hole v6 uses FTL DNS server, not dnsmasq directly
• FTLCONF environment variables configure FTL's pihole.toml
• DNS records added via web UI are not persistent (use FTLCONF_dns_hosts)
• Router must push Pi-hole DNS to clients via DHCP
• Client DNS cache can persist for hours (flush after changes)
• Use domains.toml + manage-domains.sh for automated DNS record management