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name: pihole
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description: Debug and manage a self-hosted Pi-hole v6 Docker deployment — DNS troubleshooting, database queries, whitelisting, and common failure patterns.
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category: self-hosting
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triggers:
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- "Pi-hole"
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- "pihole"
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- "DNS blocking"
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- "internet not working + Pi-hole"
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- "devices can't connect + DNS"
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---
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# Pi-hole v6 Debugging & Management
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Self-hosted Pi-hole v6 in Docker on a Linux server. Covers diagnosing DNS issues, querying the FTL database, whitelisting, and common false-positive patterns.
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See `references/v6-api-quirks.md` for Pi-hole v6 CLI/API changes, `references/query-db.py` for a reusable database query script, and `references/cname-false-positive-evidence.md` for empirical evidence of CNAME false-positive blocking patterns.
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## Quick Health Check
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```bash
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docker ps --filter name=pihole # is it running?
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docker exec pihole pihole status # FTL + blocking status
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dig +short google.com @<pihole-ip> # does DNS resolution work?
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```
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## Accessing the FTL Database
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Pi-hole v6 stores queries in `/etc/pihole/pihole-FTL.db` inside the container. The host path is under `/var/lib/docker/volumes/pihole_etc/_data/`.
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**Permission pitfall:** `/var/lib/docker` has `drwx--x---` permissions — regular users can't traverse it even if the volume files are user-owned. Copy the database out with sudo:
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```bash
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sudo cp /var/lib/docker/volumes/pihole_etc/_data/pihole-FTL.db /tmp/pihole-FTL.db
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sudo cp /var/lib/docker/volumes/pihole_etc/_data/pihole-FTL.db-wal /tmp/pihole-FTL.db-wal
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sudo cp /var/lib/docker/volumes/pihole_etc/_data/pihole-FTL.db-shm /tmp/pihole-FTL.db-shm
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sudo chown $USER:$USER /tmp/pihole-FTL.db*
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```
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Then query with Python sqlite3 (the container is Alpine — no python/sqlite3 inside):
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```python
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import sqlite3
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conn = sqlite3.connect('/tmp/pihole-FTL.db')
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cur = conn.cursor()
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cur.execute("SELECT datetime(timestamp,'unixepoch','localtime'), domain, client, status FROM queries ORDER BY id DESC LIMIT 30")
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```
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## Pi-hole v6 Status Codes
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| Code | Meaning | Notes |
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|------|---------|-------|
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| 1 | GRAVITY_BLOCKED | Domain in adlist |
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| 2 | FORWARDED | Sent to upstream DNS |
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| 3 | CACHE | Answered from cache |
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| 4 | REGEX_BLOCKED | Matches regex denylist |
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| 5 | EXACT_BLOCKED | Exact denylist match |
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| 6 | UPSTREAM_BLOCKED | Upstream returned NXDOMAIN/blocked |
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| 14 | CACHED_BLOCKED | Previously blocked, cached result — **KEY FALSE-POSITIVE SIGNAL** |
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| 17 | RETRIED | First attempt failed, retry succeeded — normal but high % = problem |
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**Status 14 is the smoking gun for false positives.** It means a domain was cached as blocked (usually via CNAME chain inspection). Essential domains like `connectivitycheck.gstatic.com` or `dns.msftncsi.com` getting status 14 will break device connectivity checks.
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## Deep CNAME Inspection False Positives
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**Symptom:** Some devices work, others don't. Android TV, Windows, and IoT devices are most affected — they have strict connectivity checks that fail on first blocked DNS response.
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**Root cause:** Pi-hole v6 has `CNAMEdeepInspect = true` by default. When a domain's CNAME chain passes through any blocked domain, the entire chain is blocked. Google infrastructure domains (`gstatic.com`, `l.google.com`, `googlehosted.com`, `1e100.net`) often end up in blocklists as subdomain entries, causing collateral damage.
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**Diagnosis:**
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```bash
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# Check if deep CNAME inspection is on
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docker exec pihole cat /etc/pihole/pihole.toml | grep CNAMEdeepInspect
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# Find domains getting status 14 (cached false blocks)
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python3 -c "
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import sqlite3; conn = sqlite3.connect('/tmp/pihole-FTL.db')
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cur = conn.cursor()
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cur.execute('SELECT domain, count(*) FROM queries WHERE status=14 GROUP BY domain ORDER BY count(*) DESC LIMIT 20')
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for d,c in cur.fetchall(): print(f'{c:5}x | {d}')
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"
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```
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**Fix — whitelist the critical domains:**
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```bash
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docker exec pihole pihole allow connectivitycheck.gstatic.com
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docker exec pihole pihole allow dns.msftncsi.com
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docker exec pihole pihole allow ota.nvidia.com
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docker exec pihole pihole allow clients3.google.com
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docker exec pihole pihole allow android.apis.google.com
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# Google Cast / Chromecast mtalk domains (alt1 through alt8)
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docker exec pihole pihole allow alt1-mtalk.google.com
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docker exec pihole pihole allow alt2-mtalk.google.com
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docker exec pihole pihole allow alt3-mtalk.google.com
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docker exec pihole pihole allow alt4-mtalk.google.com
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docker exec pihole pihole allow alt5-mtalk.google.com
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docker exec pihole pihole allow alt6-mtalk.google.com
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docker exec pihole pihole allow alt7-mtalk.google.com
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docker exec pihole pihole allow alt8-mtalk.google.com
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# Reload DNS to flush the stale block cache
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docker exec pihole pihole reloaddns
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```
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**Pi-hole v6 CLI change:** `pihole -w` (whitelist) no longer works — use `pihole allow` instead. `pihole -c` (chronometer) is also gone.
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## Common Failure Patterns
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### "Worked for a minute after restart, then died"
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- If DNS queries stop entirely (check DB): device is going to sleep or Ethernet power management is killing the connection. Check device-side power/sleep settings. Android TV: enable Developer Options → Stay Awake.
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- If status 14 appears on connectivity domains: CNAME inspection false positive (see above).
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- If status 17 rate is >30% for a device: upstream DNS or network issue.
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### Some devices have internet, some don't
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- Devices bypassing Pi-hole (hardcoded 8.8.8.8) → always work
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- Devices using Pi-hole via DHCP → affected by false blocks
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- Check which clients are querying Pi-hole vs not: compare ARP table with Pi-hole client list
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### ASUS Router DNS Director + Pi-hole = Catastrophic Overblocking
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On ASUS routers (RT-AX82U, etc.), the **DNS Director / DNS Filter** feature (under LAN settings) hijacks ALL device DNS queries and redirects them through Pi-hole. Combined with Pi-hole's deep CNAME inspection blocking Google Cast domains, this breaks:
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- Chromecast / Google Cast (Android TV, Shield) — `alt1-8-mtalk.google.com` blocked
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- Smart home devices, IoT, game consoles — many hardcode 8.8.8.8 but DNS Director captures it
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- Any device that expects unfiltered DNS for connectivity checks
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**Fix options (pick one):**
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1. **Whitelist the domains** (preferred — keeps ad blocking): allow `connectivitycheck.gstatic.com`, `clients3.google.com`, `alt1-mtalk.google.com` through `alt8-mtalk.google.com`, then `pihole reloaddns`.
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2. **Disable DNS Director globally**: ASUS LAN → DNS Director → set global rule to "Router" or "No Filtering". Pi-hole stays running; only devices manually pointed to it use it.
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3. **Per-device exemption**: DNS Director → set specific devices (Shield IP, etc.) to "No Filtering" while everyone else goes through Pi-hole.
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This is a router-level issue — not a Pi-hole bug. DNS Director is the feature that forces all traffic through Pi-hole without the user realizing it.
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### "pihole query returns nothing but domain resolves"
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- Pi-hole v6 uses a port 4711 telnet API internally. The pihole CLI may need authentication. Direct database queries are more reliable for investigation.
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## Router DHCP Setup
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The ASUS router at 192.168.50.1 should have Pi-hole set as the ONLY DNS server in DHCP settings. No secondary/fallback DNS — clients will use the fallback to bypass Pi-hole entirely when the primary is slow.
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