Troubleshooting ESPHome DNS Issues

General
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I recently encountered an issue where my ESPHome devices were not connecting properly, despite being online and showing some sensor data in Home Assistant. The logs indicated DNS problems, with the hostname logs showing NXDOMAIN errors and a different DNS server responding than expected. Here’s my journey to resolve this issue:

Understanding the Problem

  • ESPHome Version: 2022.12.8
  • Home Assistant Version: 2023.1.2
  • RPi4 Setup: Acting as a gateway with Supervisor 2023.01.1 and HACS 1.30.1

The logs revealed that DNS queries were being routed to an unexpected IP (172.30.32.1) instead of the configured 192.168.1.1. This suggested a misconfiguration in the DNS settings or an interference from another service.

Steps Taken to Diagnose

  1. DNS Configuration Check:

    • Verified that the local DNS server was correctly set to 192.168.1.1 in Home Assistant’s settings.
    • Checked the ha dns info output, which showed the fallback IP as 172.30.32.3, indicating a possible network configuration issue.

  2. Network Interface Inspection:

    • Ran ip a to ensure the correct DNS servers were assigned to the network interfaces.
    • Discovered that the RPi4 was using a different DNS resolver than intended, pointing to the unexpected 172.30.32.1.

  3. mDNS Functionality Test:

    • Since ESPHome relies on mDNS for hostname resolution, I tested mDNS using avahi-browse -r _esphome._tcp.
    • Found that mDNS was not functioning correctly, leading to failed hostname resolution.

  4. Manual DNS Resolution:

    • Used nslookup and dig commands to query the ESPHome hostnames directly.
    • Identified that the DNS server at 172.30.32.1 was not responding to these queries, confirming a DNS misconfiguration.

  5. ESPHome Configuration Review:

    • Checked the ESPHome configuration files to ensure hostnames and DNS settings were correctly specified.
    • Found no typos or configuration errors, but noted that the devices were using the default mDNS setup without explicit DNS overrides.

  6. Network Firewall Check:

    • Ensured that no firewall rules were blocking DNS queries or mDNS traffic on port 53 or 5353.
    • Confirmed that the network was allowing necessary traffic.

Resolution

After extensive troubleshooting, the issue was traced to a misconfiguration in the network settings of the RPi4. The DNS resolver was inadvertently set to use the fallback IP instead of the intended 192.168.1.1. Here’s how I fixed it:

  1. Updated Network Configuration:

    • Edited the network interface configuration file (/etc/dhcpcd.conf) to explicitly set the DNS servers.

    • Added the following lines:

      dns_server=192.168.1.1
      dns_server=8.8.8.8

  2. Restarted Networking Services:

    • Rebooted the RPi4 to apply the changes.
    • Verified the DNS settings post-reboot using ha dns info.

  3. Rebooted ESPHome Devices:

    • Powered cycled each ESPHome device to ensure they reconnected with the updated DNS settings.

Outcome

After these adjustments, the ESPHome devices successfully connected, and the hostname resolution issues were resolved. The logs no longer showed NXDOMAIN errors, and the correct DNS server (192.168.1.1) was responding to queries.

Lessons Learned

  • Always verify DNS configurations, especially in setups with multiple DNS servers.
  • Network configuration files can sometimes override intended settings, so regular audits are beneficial.
  • Testing mDNS functionality is crucial for ESPHome setups, as it relies heavily on this protocol for device discovery.

This experience underscored the importance of thorough network configuration checks and the value of manual testing tools like nslookup and dig in diagnosing connectivity issues.