En Ubuntu 22.04, los DNS se configuran por defecto con systemd.
Si usáis NetWork Manager para gestionar la red, podéis consultar los DNS recibidos vía DHCP utilizando el comando nmcli:
nmcli dev show | grep DNS
IP4.DNS[1]: 212.230.135.1
IP4.DNS[2]: 212.230.135.2
Ahora bien, si queréis consultar qué DNS tiene configurados nuestro sistema, tan sólo tenemos que usar el comando resolvectl:
resolvectl status
Global
Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub
Current DNS Server: 1.1.1.1
DNS Servers: 1.1.1.1
Fallback DNS Servers: 8.8.8.8
Link 2 (enp7s0)
Current Scopes: DNS
Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 212.230.135.1
DNS Servers: 212.230.135.1 212.230.135.2
DNS Domain: Home
En la salida anterior podéis observar que tenemos configurados varios servidores DNS. Los dos primeros (1.1.1.1 y 8.8.8.8) se encuentran configurados en el fichero /etc/systemd/resolved.conf:
# This file is part of systemd.
#
# systemd is free software; you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free
# Software Foundation; either version 2.1 of the License, or (at your option)
# any later version.
#
# Entries in this file show the compile time defaults. Local configuration
# should be created by either modifying this file, or by creating "drop-ins" in
# the resolved.conf.d/ subdirectory. The latter is generally recommended.
# Defaults can be restored by simply deleting this file and all drop-ins.
#
# Use 'systemd-analyze cat-config systemd/resolved.conf' to display the full config.
#
# See resolved.conf(5) for details.
[Resolve]
# Some examples of DNS servers which may be used for DNS= and FallbackDNS=:
# Cloudflare: 1.1.1.1#cloudflare-dns.com 1.0.0.1#cloudflare-dns.com 2606:4700:4700::1111#cloudflare-dns.com 2606:4700:4700::1001#cloudflare-dns.com
# Google: 8.8.8.8#dns.google 8.8.4.4#dns.google 2001:4860:4860::8888#dns.google 2001:4860:4860::8844#dns.google
# Quad9: 9.9.9.9#dns.quad9.net 149.112.112.112#dns.quad9.net 2620:fe::fe#dns.quad9.net 2620:fe::9#dns.quad9.net
DNS=1.1.1.1
FallbackDNS=8.8.8.8
#Domains=
#DNSSEC=no
#DNSOverTLS=no
#MulticastDNS=no
#LLMNR=no
#Cache=no-negative
#CacheFromLocalhost=no
#DNSStubListener=yes
#DNSStubListenerExtra=
#ReadEtcHosts=yes
#ResolveUnicastSingleLabel=no
En cuanto al os dos siguientes (212.230.135.1 y 212.230.135.2) son los recibidos vía DHCP.
