systemd Developer Tom Gundersen teg@jklm.no resolved.conf 5 resolved.conf resolved.conf.d Network Name Resolution configuration files /etc/systemd/resolved.conf /etc/systemd/resolved.conf.d/*.conf /run/systemd/resolved.conf.d/*.conf /usr/lib/systemd/resolved.conf.d/*.conf These configuration files control local DNS and LLMNR name resolution. DNS= A space-separated list of IPv4 and IPv6 addresses to be used as system DNS servers. DNS requests are sent to one of the listed DNS servers in parallel to any per-interface DNS servers acquired from systemd-networkd.service8. For compatibility reasons, if this setting is not specified, the DNS servers listed in /etc/resolv.conf are used instead, if that file exists and any servers are configured in it. This setting defaults to the empty list. FallbackDNS= A space-separated list of IPv4 and IPv6 addresses to be used as the fallback DNS servers. Any per-interface DNS servers obtained from systemd-networkd.service8 take precedence over this setting, as do any servers set via DNS= above or /etc/resolv.conf. This setting is hence only used if no other DNS server information is known. If this option is not given, a compiled-in list of DNS servers is used instead. Domains= A space-separated list of search domains. For compatibility reasons, if this setting is not specified, the search domains listed in /etc/resolv.conf are used instead, if that file exists and any domains are configured in it. This setting defaults to the empty list. LLMNR= Takes a boolean argument or resolve. Controls Link-Local Multicast Name Resolution support (RFC 4794) on the local host. If true, enables full LLMNR responder and resolver support. If false, disables both. If set to resolve, only resolution support is enabled, but responding is disabled. Note that systemd-networkd.service8 also maintains per-interface LLMNR settings. LLMNR will be enabled on an interface only if the per-interface and the global setting is on. MulticastDNS= Takes a boolean argument or resolve. Controls Multicast DNS support (RFC 6762) on the local host. If true, enables full Multicast DNS responder and resolver support. If false, disables both. If set to resolve, only resolution support is enabled, but responding is disabled. Note that systemd-networkd.service8 also maintains per-interface Multicast DNS settings. Multicast DNS will be enabled on an interface only if the per-interface and the global setting is on. DNSSEC= Takes a boolean argument or allow-downgrade. If true all DNS lookups are DNSSEC-validated locally (excluding LLMNR and Multicast DNS). If a response for a lookup request is detected invalid this is returned as lookup failure to applications. Note that this mode requires a DNS server that supports DNSSEC. If the DNS server does not properly support DNSSEC all validations will fail. If set to allow-downgrade DNSSEC validation is attempted, but if the server does not support DNSSEC properly, DNSSEC mode is automatically disabled. Note that this mode makes DNSSEC validation vulnerable to "downgrade" attacks, where an attacker might be able to trigger a downgrade to non-DNSSEC mode by synthesizing a DNS response that suggests DNSSEC was not supported. If set to false, DNS lookups are not DNSSEC validated. Note that DNSSEC validation requires retrieval of additional DNS data, and thus results in a small DNS look-up time penalty. DNSSEC requires knowledge of "trust anchors" to prove data integrity. The trust anchor for the Internet root domain is built into the resolver, additional trust anchors may be defined with dnssec-trust-anchors.d5. Trust anchors may change in regular intervals, and old trust anchors may be revoked. In such a case DNSSEC validation is not possible until new trust anchors are configured locally or the resolver software package is updated with the new root trust anchor. In effect, when the built-in trust anchor is revoked and DNSSEC= is true, all further lookups will fail, as it cannot be proved anymore whether lookups are correctly signed, or validly unsigned. If DNSSEC= is set to allow-downgrade the resolver will automatically turn off DNSSEC validation in such a case. Client programs looking up DNS data will be informed whether lookups could be verified using DNSSEC, or whether the returned data could not be verified (either because the data was found unsigned in the DNS, or the DNS server did not support DNSSEC or no appropriate trust anchors were known). In the latter case it is assumed that client programs employ a secondary scheme to validate the returned DNS data, should this be required. It is recommended to set DNSSEC= to true on systems where it is known that the DNS server supports DNSSEC correctly, and where software or trust anchor updates happen regularly. On other systems it is recommended to set DNSSEC= to allow-downgrade. In addition to this global DNSSEC setting systemd-networkd.service8 also maintains per-interface DNSSEC settings. For system DNS servers (see above), only the global DNSSEC setting is in effect. For per-interface DNS servers the per-interface setting is in effect, unless it is unset in which case the global setting is used instead. Site-private DNS zones generally conflict with DNSSEC operation, unless a negative (if the private zone is not signed) or positive (if the private zone is signed) trust anchor is configured for them. If allow-downgrade mode is selected, it is attempted to detect site-private DNS zones using top-level domains (TLDs) that are not known by the DNS root server. This logic does not work in all private zone setups. Defaults to off. systemd1, systemd-resolved.service8, systemd-networkd.service8, dnssec-trust-anchors.d5, resolv.conf4