mDNS — Hostname Resolution

mDNS (Multicast DNS) lets devices on the same WiFi network find each other by name (.local hostnames) without a DNS server. iROSLink advertises itself as <your-iphone-name>.local so you can use a hostname instead of a raw IP.

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Platform support

Platform	mDNS support	Notes
macOS	Built-in	Works immediately
Linux	Built-in (avahi)	avahi-daemon runs by default on most distros
Windows	Requires install	Install Bonjour (bundled with iTunes or Apple Devices app)
iOS / Android	Built-in	Works immediately

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Test mDNS resolution with ping

Before connecting Foxglove or your ESP32, verify the hostname resolves from your machine.

macOS / Linux

ping -c 4 myphone.local

Expected output:

PING myphone.local (192.168.1.42): 56 data bytes
64 bytes from 192.168.1.42: icmp_seq=0 ttl=64 time=3.2 ms
64 bytes from 192.168.1.42: icmp_seq=1 ttl=64 time=2.8 ms
...

The IP address in the parentheses (192.168.1.42) is what mDNS resolved to. Use that IP directly if you ever need to bypass mDNS.

Stop ping with Ctrl+C.

Windows (PowerShell)

ping myphone.local

If Bonjour is installed and the phone is on the same network you'll see replies. If you see Ping request could not find host myphone.local, Bonjour is not installed or the phone is on a different subnet.

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Common failures

ping: cannot resolve myphone.local: Name or service not known
→ mDNS not available. On Linux, check systemctl status avahi-daemon. On Windows, install Bonjour.

Timeout (no reply, no error)
→ Hostname resolved but phone is blocking ICMP. Rare on iOS. More likely the hostname resolved to the wrong IP — check that phone and computer are on the same WiFi network (not one on 2.4 GHz and the other on 5 GHz with client isolation enabled).

Wrong IP resolved
→ Stale mDNS cache. Flush it:

# macOS
sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder

# Linux
sudo systemctl restart avahi-daemon

IP changes after reboot
→ DHCP assigns a new IP. mDNS always resolves to the current IP — use the .local hostname everywhere instead of hardcoding an IP. If the ESP32 uses a hardcoded IP for the Zenoh router, set a DHCP reservation for the phone's MAC address in your router settings.

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Find the phone's hostname

The hostname is your iPhone's name (Settings → General → About → Name) with spaces replaced by hyphens and .local appended. Example: "Quoc's iPhone" → quocs-iphone.local.

iROSLink also shows the full address in Settings → Foxglove WebSocket Server and Settings → ROS2 Bridge (Zenoh).

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Using iPhone Hotspot

iPhone hotspot is often the most reliable WiFi option — the phone acts as its own router with a direct connection to the ESP32, eliminating any home router quality issues.

Setup:

1. On iPhone: Settings → Personal Hotspot → Allow Others to Join → toggle on
2. Set a hotspot password you'll remember
3. On the ESP32, update secret.h with the hotspot credentials (→ full secret.h setup):

   #define WIFI_NETWORKS \
       { "Your iPhone Name", "yourpassword" }   // iPhone name exactly as shown in Settings
   
   #define ROUTER_MDNS_HOST "iphone"   // phone mDNS name — fallback IP 172.20.10.1 used if mDNS fails
   

4. Re-flash the ESP32 (→ flash instructions)
5. In iROSLink → Settings → ROS2 Bridge (Zenoh): select Router mode — your phone's hotspot IP (172.20.10.1) is shown there

mDNS on hotspot

mDNS (.local hostnames) may not resolve reliably on some ESP32 or desktop clients connected via hotspot. If peer count stays 0, use the raw IP 172.20.10.1 in ZENOH_ROUTER instead of the mDNS hostname.

Battery note

Running hotspot + iROSLink simultaneously drains the battery faster. Plug into USB power if doing long sessions.

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Back to setup

→ Sensor Preview — connect Foxglove
→ Build & Configure — configure Zenoh
→ Troubleshooting — connection issues