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00-resolved-no_dns.conf
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00-resolved-no_dns.conf
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# CACHE
# Takes a boolean or "no-negative" as argument. If "yes" (the default), resolving a domain name which already got queried earlier will return the previous result as long as it is still valid, and thus does not result in a new network
# request. Be aware that turning off caching comes at a performance penalty, which is particularly high when DNSSEC is used. If "no-negative", only positive answers are cached.
# Default: yes
Cache=yes
# CACHE FROM LOCALHOST
# Takes a boolean as argument. If "no" (the default), and response comes from host-local IP address (such as 127.0.0.1 or ::1), the result wouldn't be cached in order to avoid potential duplicate local caching.
# Default: no
CacheFromLocalhost=no
# MULTICAST DNS
# Takes a boolean argument or "resolve". Controls Multicast DNS support (RFC 6762[2]) 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.service(8) also maintains per-link Multicast DNS settings. Multicast DNS will be enabled on a link only if the per-link and the global setting is on.
# Default: no
MulticastDNS=no
# DNS OVER TLS
# Takes a boolean argument or "opportunistic". If true all connections to the server will be encrypted. Note that this mode requires a DNS server that supports DNS-over-TLS and has
# a valid certificate. If the hostname was specified in DNS= by using the format "address#server_name" it is used to validate its certificate and also to enable Server Name Indication
# (SNI) when opening a TLS connection. Otherwise the certificate is checked against the server's IP. If the DNS server does not support DNS-over-TLS all DNS requests will fail.
# When set to "opportunistic" DNS request are attempted to send encrypted with DNS-over-TLS. If the DNS server does not support TLS, DNS-over-TLS is disabled. Note that this mode
# makes DNS-over-TLS vulnerable to "downgrade" attacks, where an attacker might be able to trigger a downgrade to non-encrypted mode by synthesizing a response that suggests
# DNS-over-TLS was not supported. If set to false, DNS lookups are send over UDP.
# Note that DNS-over-TLS requires additional data to be send for setting up an encrypted connection, and thus results in a small DNS look-up time penalty.
# Note that in "opportunistic" mode the resolver is not capable of authenticating the server, so it is vulnerable to "man-in-the-middle" attacks.
# In addition to this global DNSOverTLS= setting systemd-networkd.service(8) also maintains per-link DNSOverTLS= settings. For system DNS servers (see above),
# only the global DNSOverTLS= setting is in effect. For per-link DNS servers the per-link setting is in effect, unless it is unset in which case the global setting is used instead.
# Default: no
DNSOverTLS=no
# DNSSEC
# Takes a boolean argument or "allow-downgrade".
# If set to true, all DNS lookups are DNSSEC-validated locally (excluding LLMNR and Multicast DNS). If the response to a lookup request is detected to be invalid a lookup failure is
#returned 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. In this mode, or when set to "allow-downgrade" and the downgrade has happened, the resolver becomes security-unaware and all
# forwarded queries have DNSSEC OK (DO) bit unset.
# Note that DNSSEC validation requires retrieval of additional DNS data, and thus results in a small DNS lookup 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.d(5). Trust anchors may change at 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.service(8) also maintains per-link DNSSEC settings. For system DNS servers (see above), only the global
# DNSSEC setting is in effect. For per-link DNS servers the per-link setting is in effect, unless it is unset in whic 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.
# Default: allow-downgrade
DNSSEC=allow-downgrade
# DNS STUB LISTENER
# Takes a boolean argument or one of "udp" and "tcp". If "udp", a DNS stub resolver will listen for UDP requests on addresses 127.0.0.53 and 127.0.0.54, port 53. If "tcp", the stub will
# listen for TCP requests on the same addresses and port. If "yes" (the default), the stub listens for both UDP and TCP requests. If "no", the stub listener is disabled.
# The DNS stub resolver on 127.0.0.53 provides the full feature set of the local resolver, which includes offering LLMNR/MulticastDNS resolution. The DNS stub resolver on
# 127.0.0.54 provides a more limited resolver, that operates in "proxy" mode only, i.e. it will pass most DNS messages relatively unmodified to the current upstream DNS servers and
# back, but not try to process the messages locally, and hence does not validate DNSSEC, or offer up LLMNR/MulticastDNS. (It will translate to DNS-over-TLS communication if needed however.)
# Note that the DNS stub listener is turned off implicitly when its listening address and port are already in use.
# Default: yes
DNSStubListener=yes
# DNS STUB LISTENER EXTRA
# Takes an IPv4 or IPv6 address to listen on. The address may be optionally prefixed with a protocol name ("udp" or "tcp")
# separated with ":". If the protocol is not specified, the service will listen on both UDP and TCP. It may be also
# optionally suffixed by a numeric port number with separator ":". When an IPv6 address is specified with a port number,
# then the address must be in the square brackets. If the port is not specified, then the service uses port 53. Note that
# this is independent of the primary DNS stub configured with DNSStubListener=, and only configures additional sockets to
# listen on. This option can be specified multiple times. If an empty string is assigned, then the all previous assignments
# are cleared. Defaults to unset.
# Examples:
# DNSStubListenerExtra=192.168.10.10
# DNSStubListenerExtra=2001:db8:0:f102::10
# DNSStubListenerExtra=192.168.10.11:9953
# DNSStubListenerExtra=[2001:db8:0:f102::11]:9953
# DNSStubListenerExtra=tcp:192.168.10.12
# DNSStubListenerExtra=udp:2001:db8:0:f102::12
DNSStubListenerExtra=
# DOMAINS
# A space-separated list of domains, optionally prefixed with "~", used for two distinct purposes described below. Defaults to the empty list.
# Any domains not prefixed with "~" are used as search suffixes when resolving single-label hostnames (domain names which contain no dot), in order to qualify them into
# fully-qualified domain names (FQDNs). These "search domains"
# are strictly processed in the order they are specified in, until the name with the suffix appended is found. For compatibility reasons, if this setting is not specified, the
# search domains listed in /etc/resolv.conf with the search keyword are used instead, if that file exists and any domains are configured in it.
# The domains prefixed with "~" are called "route-only domains". All domains listed here (both search domains and route-only domains after removing the "~" prefix) define a
# search path that preferably directs DNS queries to this interface. This search path has an effect only when suitable per-link DNS servers are known. Such servers may be defined
# through the DNS= setting (see above) and dynamically at run time, for example from DHCP leases. If no per-link DNS servers are known, route-only domains have no effect.
# Use the construct "~." (which is composed from "~" to indicate a route-only domain and "." to indicate the DNS root domain that is the implied suffix of all DNS domains) to
# use the DNS servers defined for this link preferably for all domains.
# See "Protocols and Routing" in systemd-resolved.service(8) for details of how search and route-only domains are used.
# Note that configuring the MulticastDNS domain "local" as search or routing domain has the effect of routing lookups
# for this domain to classic unicast DNS. This may be used to provide compatibility with legacy installations that use this
# domain in a unicast DNS context, against the IANA assignment of this domain to pure MulticastDNS purposes. Search and
# routing domains are a unicast DNS concept, they cannot be used to resolve single-label lookups via MulticastDNS.
# Default:
Domains=
# LLMNR
# Takes a boolean argument or "resolve". Controls Link-Local Multicast Name Resolution support (RFC 4795[1]) 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.service(8) also maintains per-link LLMNR settings. LLMNR will be enabled on a link only if the
# per-link and the global setting is on.
# Default: no
LLMNR=no
# READ ETC HOSTS
# Takes a boolean argument. If "yes" (the default), systemd-resolved will read /etc/hosts, and try to resolve hosts or address by using the entries in the file before
# sending query to DNS servers.
# Default: yes
ReadEtcHosts=yes
# RESOLVE UNICAST SINGLE LABEL
# Takes a boolean argument. When false (the default), systemd-resolved will not resolve A and AAAA queries for single-label names over classic DNS. Note that such names may
# still be resolved if search domains are specified (see Domains= above), or using other mechanisms, in particular via LLMNR or from /etc/hosts. When true, queries for single-label
# names will be forwarded to global DNS servers even if no search domains are defined.
# This option is provided for compatibility with configurations where public DNS servers are not used. Forwarding single-label names to servers not under your control is not
# standard-conformant, see IAB Statement[3], and may create a privacy and security risk.
# Default: no
ResolveUnicastSingleLabel=no
# STALE RETENTION SEC
# Takes a duration value, which determines the length of time DNS resource records can be retained in the cache beyond their Time To Live (TTL). This allows these records to be
# returned as stale records. By default, this value is set to zero, meaning that DNS resource records are not stored in the cache after their TTL expires.
# This is useful when a DNS server failure occurs or becomes unreachable. In such cases, systemd-resolved(8) continues to use the stale records to answer DNS queries, particularly
# when no valid response can be obtained from the upstream DNS servers. However, this doesn't apply to NXDOMAIN responses, as those are still perfectly valid responses. This feature
# enhances resilience against DNS infrastructure failures and outages.
# systemd-resolved always attempts to reach the upstream DNS servers first, before providing the client application with any stale data. If this feature is enabled, cache will not be
# flushed when changing servers.
# Default=0
StaleRetentionSec=0