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# Split-Horizon DNS Implementation Guide
Last updated: 2026-03-20
## Problem
All DNS queries for `*.vish.gg`, `*.thevish.io`, and `*.crista.love` currently resolve to Cloudflare proxy IPs (104.21.x.x), even when the client is on the same LAN as the services. This means:
1. **Hairpin NAT** — LAN traffic goes out to Cloudflare and back in through the router
2. **Internet dependency** — if the WAN link goes down, LAN services are unreachable by domain
3. **Added latency** — ~50ms roundtrip through Cloudflare vs ~1ms on LAN
4. **Cloudflare bottleneck** — all traffic proxied through CF even when unnecessary
## Solution
**Status: IMPLEMENTED (2026-03-20)**
Use AdGuard Home on Calypso (primary) and Atlantis (backup) as **split-horizon DNS resolvers** that return local IPs for homelab domains when queried from the LAN, while external clients continue to use Cloudflare.
```
┌──────────────────────────────────┐
│ DNS Query for │
│ nb.vish.gg │
└───────────────┬──────────────────┘
┌───────────────▼──────────────────┐
│ Where is the client? │
└───────┬───────────────┬──────────┘
│ │
LAN Client External Client
│ │
▼ ▼
┌──────────────┐ ┌──────────────┐
│ AdGuard Home │ │ Cloudflare │
│ (Calypso + │ │ DNS │
│ Atlantis) │ │ │
│ Returns: │ │ Returns: │
│100.85.21.51 │ │ 104.21.73.214│
│(NPM Tailscale)│ │ (CF proxy) │
└──────┬───────┘ └──────┬───────┘
│ │
▼ ▼
┌──────────────┐ ┌──────────────┐
│ NPM (local) │ │ Cloudflare │
│ matrix-ubuntu│ │ → WAN IP │
│ :443 ~1ms │ │ → NPM │
└──────┬───────┘ │ ~50ms │
│ └──────┬───────┘
▼ ▼
┌─────────────────────────────────┐
│ Backend Service │
│ (same result, faster path) │
└─────────────────────────────────┘
```
## Prerequisites
NPM is now on matrix-ubuntu (192.168.0.154) listening on standard ports 80/443/81. The migration from Calypso was completed on 2026-03-20.
| Port | Status |
|------|--------|
| 80:80 | **Active** |
| 443:443 | **Active** |
| 81:81 | **Active** (Admin UI) |
## Implementation Steps
### Step 1: Move NPM to Standard Ports -- DONE
NPM migrated from Calypso to matrix-ubuntu (192.168.0.154) on 2026-03-20. Compose file: `hosts/vms/matrix-ubuntu/nginx-proxy-manager.yaml`. Host nginx on matrix-ubuntu has been disabled (`systemctl disable nginx`); NPM now handles mastodon.vish.gg, mx.vish.gg, and mm.crista.love directly.
Router port forwards updated:
- `WAN:443 → 192.168.0.154:443`
- `WAN:80 → 192.168.0.154:80`
### Step 2: Configure AdGuard DNS Rewrites -- DONE
AdGuard DNS rewrites configured on both Calypso (http://192.168.0.250:9080) and Atlantis (http://192.168.0.200:9080). Wildcard entries point to NPM's Tailscale IP:
| Domain | Answer | Notes |
|--------|--------|-------|
| `*.vish.gg` | `100.85.21.51` | All vish.gg domains → NPM Tailscale IP |
| `*.thevish.io` | `100.85.21.51` | All thevish.io domains → NPM Tailscale IP |
| `*.crista.love` | `100.85.21.51` | All crista.love domains → NPM Tailscale IP |
These three wildcards cover all 36 proxy hosts. AdGuard resolves matching queries locally instead of forwarding to upstream DNS.
**Exceptions** — these domains need direct IPs (not NPM), added as specific overrides:
| Domain | Answer | Reason |
|--------|--------|--------|
| `mx.vish.gg` | `192.168.0.154` | Matrix federation needs direct access on port 8448 |
| `derp.vish.gg` | `192.168.0.250` | DERP relay — direct IP, no CF proxy |
| `derp-atl.vish.gg` | `192.168.0.200` | Atlantis DERP relay |
| `headscale.vish.gg` | `192.168.0.250` | Headscale control — direct access |
| `turn.thevish.io` | `192.168.0.200` | TURN/STUN needs direct UDP |
**.tail.vish.gg overrides** — specific rewrites to override the wildcard for Tailscale-specific subdomains.
Specific entries take priority over wildcards in AdGuard.
### Step 3: Set AdGuard as LAN DNS Server -- DONE
Router (Archer BE800) DHCP configured with dual AdGuard DNS:
1. **Primary DNS:** `192.168.0.250` (Calypso AdGuard)
2. **Secondary DNS:** `192.168.0.200` (Atlantis AdGuard, backup)
### Step 4: Configure Atlantis AdGuard (Backup DNS) -- DONE
Same DNS rewrites added to Atlantis's AdGuard instance (http://192.168.0.200:9080) as backup:
- Same wildcard rewrites as Calypso (pointing to `100.85.21.51`)
- Reachable at `192.168.0.200`
### Step 5: Test
```bash
# Verify local resolution
dig nb.vish.gg @192.168.0.250
# Expected: 192.168.0.250 (NPM local IP)
# Verify external resolution still works
dig nb.vish.gg @1.1.1.1
# Expected: 104.21.73.214 (Cloudflare proxy)
# Test HTTPS access via local DNS
curl -s --resolve "nb.vish.gg:443:192.168.0.250" https://nb.vish.gg/ -o /dev/null -w "%{http_code} %{time_total}s\n"
# Expected: 200 in ~0.05s (vs ~0.15s through Cloudflare)
# Test all domains resolve locally
for domain in nb.vish.gg gf.vish.gg git.vish.gg sso.vish.gg dash.vish.gg; do
ip=$(dig +short $domain @192.168.0.250 | tail -1)
echo "$domain$ip"
done
```
## SSL Considerations
**Resolved:** NPM now uses **Let's Encrypt wildcard certificates** (DNS challenge via Cloudflare API) instead of Cloudflare Origin certs. This means:
- Certs are trusted by all browsers, whether traffic comes through Cloudflare or directly via LAN
- No browser warnings for split-horizon DNS LAN access
- Certs auto-renew via NPM's built-in Let's Encrypt integration
## What Changes for Each Path
### LAN Client
```
Browser → nb.vish.gg
→ AdGuard DNS: 100.85.21.51 (NPM Tailscale IP)
→ NPM (matrix-ubuntu:443) → SSL termination (LE wildcard cert)
→ Proxy to backend (192.168.0.210:8443)
→ Response (~1ms total DNS+proxy)
```
### External Client
```
Browser → nb.vish.gg
→ Cloudflare DNS: 104.21.73.214
→ Cloudflare proxy → WAN IP → Router
→ NPM (matrix-ubuntu:443) → SSL termination
→ Proxy to backend (192.168.0.210:8443)
→ Response (~50ms total)
```
### Internet Down
```
Browser → nb.vish.gg
→ AdGuard DNS: 100.85.21.51 (cached/local)
→ NPM (matrix-ubuntu:443) → SSL termination
→ Proxy to backend
→ Response (services still work!)
```
## Current NPM Proxy Hosts (for reference)
All 36 domains that would benefit from split-horizon:
### vish.gg (27 domains)
| Domain | Backend |
|--------|---------|
| actual.vish.gg | calypso:8304 |
| cal.vish.gg | atlantis:12852 |
| dash.vish.gg | atlantis:7575 |
| dav.vish.gg | calypso:8612 |
| docs.vish.gg | calypso:8777 |
| gf.vish.gg | homelab-vm:3300 |
| git.vish.gg | calypso:3052 |
| headscale.vish.gg | calypso:8085 |
| kuma.vish.gg | rpi5:3001 |
| mastodon.vish.gg | matrix-ubuntu:3000 |
| mx.vish.gg | matrix-ubuntu:8082 |
| nb.vish.gg | homelab-vm:8443 |
| npm.vish.gg | calypso:81 |
| ntfy.vish.gg | homelab-vm:8081 |
| ollama.vish.gg | atlantis:11434 |
| ost.vish.gg | calypso:3000 |
| paperless.vish.gg | calypso:8777 |
| pt.vish.gg | atlantis:10000 |
| pw.vish.gg | atlantis:4080 |
| rackula.vish.gg | calypso:3891 |
| retro.vish.gg | calypso:8025 |
| rx.vish.gg | calypso:9751 |
| rxdl.vish.gg | calypso:9753 |
| scrutiny.vish.gg | homelab-vm:8090 |
| sf.vish.gg | calypso:8611 |
| sso.vish.gg | calypso:9000 |
| wizarr.vish.gg | atlantis:5690 |
### thevish.io (5 domains)
| Domain | Backend |
|--------|---------|
| binterest.thevish.io | homelab-vm:21544 |
| hoarder.thevish.io | homelab-vm:3482 |
| joplin.thevish.io | atlantis:22300 |
| matrix.thevish.io | matrix-ubuntu:8081 |
| meet.thevish.io | atlantis:5443 |
### crista.love (2 domains)
| Domain | Backend |
|--------|---------|
| crista.love | guava:28888 |
| cocalc.crista.love | guava:8080 |
| mm.crista.love | matrix-ubuntu:8065 |
## Rollback
If something breaks:
1. Change router DHCP DNS back to `1.1.1.1` / `8.8.8.8`
2. Or remove the DNS rewrites from AdGuard
3. All traffic reverts to Cloudflare path immediately
## Related Documentation
- [NPM Migration](npm-migration-jan2026.md) — Reverse proxy configuration
- [Authentik SSO](authentik-sso.md) — Forward auth depends on NPM routing
- [Cloudflare DNS](cloudflare-dns.md) — External DNS records
- [Image Update Guide](../admin/IMAGE_UPDATE_GUIDE.md) — Mentions Gitea/NPM as bootstrap dependencies