UniFi Lab 08
mDNS casting across VLANs
Internet works on IoT. Phone still cannot find the TV. Discovery needs mDNS Proxy across VLANs.
Your job: turn mDNS Proxy to Auto (or Custom with LAN and IoT). Keep IoT → LAN denied. Do not open the firewall to fix casting.
Run: mDNS Proxy off · Multicast Filtering off · IoT → LAN deny
Lab complete. Phone finds the TV. IoT → LAN stays denied.
cast_finds_tvCast finds TV across VLANsPath and discovery
Trunk locked healthy- GatewaymDNS Proxy OffOnline
- Trunk healthyNative LAN · Tagged IoT 30
- Switch + APWiFi Multicast Filtering OffOK
- WiFi · Default / LANUnicast and multicast pass
- LAN phoneSender · Default / LANSearching · TV not found
- mDNS discovery · LAN to IoTStops at the VLAN edge
- IoT TV / ChromecastSTOPCast target · VLAN 30 · Internet OKTV not found · mDNS Proxy Off
Discovery LAN phone to IoT TV
| Setting | Now | Need |
|---|---|---|
| mDNS Proxy | Off | Auto or Custom |
| Networks in proxy | None | LAN + IoT |
| Multicast Filtering | Off | Off |
| Discovery | TV not found | AirPlay / Cast |
| IoT internet | OK | Preset |
| IoT → LAN | Denied | Stay denied |
mDNS Proxy Off · discovery stops at the VLAN edge
IoT TV
VLAN 30 · preset healthy| IP | 192.168.30.50 |
|---|---|
| DHCP / DNS | OK |
| Internet | Online |
| IoT → Gateway | Allow (preset) |
| IoT → External | Allow (preset) |
| LAN reach | Denied |
| Seen by phone | No |
Legend
- Healthy / TV found
- TV not found / proxy Off
- LAN exposed (blocks win)
Controls
IoT → Gateway and IoT → External stay preset Allow. Discovery settings and IoT → LAN only.
Custom services, teaching labels
Out of scope for this lab
Why this fails
mDNS Proxy OffTV not found · AirPlay unavailable
After you isolate IoT, unicast internet can work while multicast discovery dies at the VLAN edge. Turn mDNS Proxy to Auto, or Custom with both networks. Do not open IoT → LAN to make casting work.
Why Broken and Fixed
Console words
- TV not foundPhone search shows no AirPlay or Cast target.Showing
- mDNS Proxy OffSettings · mDNS Proxy = Off.Showing
- Custom missing networkCustom lists LAN only or IoT only.Clear
- Multicast Filtering OnSSID drops wired to wireless multicast.Clear
- LAN exposedIoT → LAN allowed. Blocks the win.Clear
- Cast finds TV across VLANsProxy on both networks. LAN denied.Clear
Before and after
Diff rows marked| Setting or symptom | Broken start | Now |
|---|
Gear in this lab
- 1 Cloud Gateway / UDM class
- 1 Switch + AP
- 1 Phone on LAN
- 1 TV / Chromecast on IoT VLAN 30
Config only. Counts only, no prices.
Takeaway
Proxy discovery. Keep isolation.
After IoT isolation, unicast internet can work while multicast discovery dies. Turn mDNS Proxy to Auto or Custom with both networks. Do not open IoT → LAN to make casting work.
- Leave IoT → Gateway and External allowed (Lab 07).
- Turn mDNS Proxy to Auto, or Custom with LAN and IoT.
- Keep WiFi Multicast Filtering Off on the cast path.
- Keep IoT → LAN denied. Isolation stays.
Want casting and IoT isolation designed for your place? We plan that as part of a UniFi install.
Related labs
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A teaching lab, not a quote and not a design for your site. Settings are simplified from the UniFi Network app. No account, and nothing from this lab is saved.