¶ How to Add Multiple DNS Servers on OPNsense
This option exist in this submenu:
Services > ISC DHCPv4 > LAN
According to RFC 2132 3.8, use option "6". The minimum length is 4 octets, and the length must always be a multiple of 4 octets. Servers should be listed in order of preference.
¶ Steps to Add Multiple DNS Servers
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Convert IP Addresses to Hexadecimal:
Convert the individual IP addresses you want to use to their hexadecimal equivalents. Here are some examples:
- 192.168.0.1 =
c0:a8:00:01 - 192.168.0.2 =
c0:a8:00:02 - 192.168.0.3 =
c0:a8:00:03
Some tools use periods (.) instead of colons ( : ). Ensure you replace any symbol with colons ( : ).
- 192.168.0.1 =
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Concatenate the Hexadecimal Values:
In the order of server preference, concatenate the hex values together using colons ( : ) as the separator. For example:
- 192.168.0.1 + 192.168.0.2 + 192.168.0.3 =
c0:a8:00:01:c0:a8:00:02:c0:a8:00:03
- 192.168.0.1 + 192.168.0.2 + 192.168.0.3 =
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Configure OPNsense:
- In the OPNsense GUI, navigate to the DHCPv4 configuration.
- Leave the GUI option for DNS Servers blank.
- Expand Additional Options.
- Input
6into the Number field. - Change the Type to
string. - Enter the concatenated string into the Value field, e.g.,
c0:a8:00:01:c0:a8:00:02:c0:a8:00:03. - Save the configuration.
As you can view in the screen, in this example we have entered 3 DNS, so: 1.1.1.1 - 8.8.8.8 = 8.8.4.4
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Renew IP Address:
After saving the configuration, renew the IP address to apply the changes. In Windows, you can do this by running the following commands in the Command Prompt:
ipconfig /renew ipconfig /all