dnsmasq fails to resolve host with SERVFAIL

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Environment

SUSE Linux Enterprise Server 15 SP2

SUSE Linux Enterprise Server 15 SP3

Situation

After upgrading dnsmasq from version 2.78 to 2.86 name resolution fails with SERVFAIL when dnssec is enabled in the configuration.

Resolution

Enable DNSSEC on DNS forwarders (the name servers in /etc/resolv.conf) or remove 'dnssec' from the dnsmasq config file to turn dnssec off completely (default).

Cause

Dnsmasq have changed the default value for 'dnssec-check-unsigned', which is now turned on by default.

Versions of dnsmasq prior to 2.80 defaulted to not checking unsigned replies, and used '--dnssec-check-unsigned' to switch this on.

The new default is because switching off checking for unsigned replies is inherently dangerous. Not only does it open the possiblity of forged replies, but it allows everything to appear to be working even when the upstream namesevers do not support DNSSEC, and in this case no DNSSEC validation at all is occurring.

Status

Reported to Engineering

Additional Information

When 'dnssec-check-unsigned=no' is used together with 'dnssec' then zone validation will not be performed, which defeats the purpose of dnssec. The setting still exists for compatibility reasons, but it should not be used anymore. The default shipped configuration comes with dnssec off, which is basically the result of using the above two options together.

Disclaimer

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