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Hi meyergru,
Thank you for the direct feedback. You are right; my initial post was far too vague. I apologise for that. I've been troubleshooting this all day and was getting frustrated. Let me provide a proper, detailed breakdown of the situation, the hardware, the steps I've taken, and where I am now stuck.
System Information:
OPNsense Version: The latest stable version as of August 24, 2026. This problem started immediately after I ran the update from the GUI.
Hardware: This is a physical appliance, not a VM. It's a custom-built N100 box with 4x Intel i226-V 2.5GbE ports.
ISP: Plusnet (UK) on a Fibre connection.
Network Layout: The core design is OPNsense -> Managed Switch -> Devices. VLANs are used for TRUSTED and UNTRUSTED networks. This setup was working perfectly before the update.
Current Problem: OPNsense DNS Resolution is Broken
This is where I am currently stuck.
I can successfully ping 8.8.8.8 from Interfaces > Diagnostics > Ping. This proves the firewall has a valid route to the internet.
However, if I try to ping a hostname like google.com, it fails with the error: cannot resolve google.com: Host name lookup failure.
4. Attempted Forcing Upstream DNS.
To fix the DNS issue, I went to System > Settings > General.
I manually entered 8.8.8.8 and 1.1.1.1 as DNS servers.
I unchecked the box Allow DNS server list to be overridden by DHCP/PPP on WAN.
Result: No change. OPNsense itself still cannot resolve any external hostnames, even though it can ping external IPs.
5. Attempted Fix Reconfiguring DHCP.
I noticed that the update introduced Kea DHCP, and the old ISC DHCP is now marked as legacy. I assume this is part of the problem.
I tried to configure Kea DHCP (Services > Kea DHCP > Subnets) for my TRUSTED VLAN (192.168.86.0/24). I created the subnet and added an IP pool (192.168.86.100 - 200).
Here is a critical issue: In the "Edit Subnet" screen for Kea, there are no input fields for "DNS servers" or "Routers" as some guides suggest there should be. The fields are simply missing from the GUI.
Summary of Current State:
WAN is UP and has a public IP.
OPNsense CAN ping external IP addresses (e.g., 8.8.8.8).
OPNsense CANNOT resolve any DNS hostnames (e.g., google.com).
Because the firewall's resolver is broken, none of my internal clients can access the internet.
The new Kea DHCP service seems to be missing key configuration options in its interface.
My Specific Question:
Why would OPNsense be unable to perform DNS lookups, even when public DNS servers are explicitly defined in the general settings and the WAN connection is confirmed to be working? Could this be a bug in the latest version related to Unbound DNS, or is there another setting I'm missing that would cause this behavior?
Thank you for your time and expertise. The failing ping diagnostics, my general DNS settings, and the Kea DHCP subnet page that is missing the router/DNS option fields.
Thank you for the direct feedback. You are right; my initial post was far too vague. I apologise for that. I've been troubleshooting this all day and was getting frustrated. Let me provide a proper, detailed breakdown of the situation, the hardware, the steps I've taken, and where I am now stuck.
System Information:
OPNsense Version: The latest stable version as of August 24, 2026. This problem started immediately after I ran the update from the GUI.
Hardware: This is a physical appliance, not a VM. It's a custom-built N100 box with 4x Intel i226-V 2.5GbE ports.
ISP: Plusnet (UK) on a Fibre connection.
Network Layout: The core design is OPNsense -> Managed Switch -> Devices. VLANs are used for TRUSTED and UNTRUSTED networks. This setup was working perfectly before the update.
Current Problem: OPNsense DNS Resolution is Broken
This is where I am currently stuck.
I can successfully ping 8.8.8.8 from Interfaces > Diagnostics > Ping. This proves the firewall has a valid route to the internet.
However, if I try to ping a hostname like google.com, it fails with the error: cannot resolve google.com: Host name lookup failure.
4. Attempted Forcing Upstream DNS.
To fix the DNS issue, I went to System > Settings > General.
I manually entered 8.8.8.8 and 1.1.1.1 as DNS servers.
I unchecked the box Allow DNS server list to be overridden by DHCP/PPP on WAN.
Result: No change. OPNsense itself still cannot resolve any external hostnames, even though it can ping external IPs.
5. Attempted Fix Reconfiguring DHCP.
I noticed that the update introduced Kea DHCP, and the old ISC DHCP is now marked as legacy. I assume this is part of the problem.
I tried to configure Kea DHCP (Services > Kea DHCP > Subnets) for my TRUSTED VLAN (192.168.86.0/24). I created the subnet and added an IP pool (192.168.86.100 - 200).
Here is a critical issue: In the "Edit Subnet" screen for Kea, there are no input fields for "DNS servers" or "Routers" as some guides suggest there should be. The fields are simply missing from the GUI.
Summary of Current State:
WAN is UP and has a public IP.
OPNsense CAN ping external IP addresses (e.g., 8.8.8.8).
OPNsense CANNOT resolve any DNS hostnames (e.g., google.com).
Because the firewall's resolver is broken, none of my internal clients can access the internet.
The new Kea DHCP service seems to be missing key configuration options in its interface.
My Specific Question:
Why would OPNsense be unable to perform DNS lookups, even when public DNS servers are explicitly defined in the general settings and the WAN connection is confirmed to be working? Could this be a bug in the latest version related to Unbound DNS, or is there another setting I'm missing that would cause this behavior?
Thank you for your time and expertise. The failing ping diagnostics, my general DNS settings, and the Kea DHCP subnet page that is missing the router/DNS option fields.
