Android Emulator

Android Emulator

On a stock emulator, mDNS works inside the emulator only. Its virtual network doesn't reach other devices' multicast (Android's documentation: "The emulator does not support IGMP", see emulator networking), so services on your computer or local network are not found.

On a stock emulator	Works?
Publish a service and discover it from the same emulator (NSD and DNSSD)	Yes
List service types with DNSSD (the emulator's own services)	Yes
Discover services on your computer or local network	No

This is enough to test your app's code: publish a test service from the app (or another app on the emulator) and scan for it.

await zeroconf.publishService({ type: 'http', protocol: 'tcp', name: 'Emulator test', port: 8080 })
zeroconf.scan({ type: 'http' })

To discover real devices, test on a physical device on the same network as the services, or use the advanced setup below.

Advanced: TAP bridged networking (Linux, Ethernet)

Only if you really need the emulator. Read the caveats first:

• Use a Google APIs system image, not Google Play: Play images don't allow adb root, which is needed to configure eth1.
• Always start with -no-snapshot-load, otherwise the saved state ignores the QEMU network device and eth1 does not exist.
• The configuration does not persist: redo step 3 after every emulator restart.
• One emulator per TAP interface (create tap1, tap2... for more).
• Use addresses from your subnet in place of the examples.
• Wi-Fi bridging does not work on most systems. Use Ethernet.

1. Create the TAP interface and bridge (once)

sudo ip tuntap add dev tap0 mode tap user $USER
sudo ip link add name br0 type bridge
sudo ip link show                                  # find your Ethernet interface
sudo ip link set <your-ethernet-interface> master br0   # e.g. enp3s0
sudo ip link set tap0 master br0
sudo ip link set dev tap0 up
sudo ip link set dev br0 up
sudo dhcpcd br0                                    # or: sudo dhclient br0

2. Start the emulator on the TAP interface

emulator -avd <avd_name> \
  -no-snapshot-load \
  -qemu \
  -netdev tap,id=mynet0,ifname=tap0,script=no,downscript=no \
  -device virtio-net-pci,netdev=mynet0

3. Configure eth1 in the emulator

adb root
adb shell ip link set eth1 up
adb shell ip addr add <unused_ip> dev eth1              # e.g. 192.168.1.213/24
adb shell ip route add default via <gateway> dev eth1   # e.g. 192.168.1.1
adb shell ping -c 2 <device_ip>                          # check connectivity

4. Point Metro at the bridge address

ip addr show br0 | grep "inet "      # e.g. inet 192.168.1.28/24
REACT_NATIVE_PACKAGER_HOSTNAME=192.168.1.28 npx expo start --android