Outbound DNS on my server is broken. Where to fix it?

Posted on September 19, 2022
DNS
Asked by sven

Started with not being able to renew Certbot, which hinted at that I generally can’t resolve outgoing DNS from my server.

nslookup acme-v02.api.letsencrypt.org
nslookup amazon.com
i.e. simply fail.
Any idea how and where to fix that?


           
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                 KFSys
                
                
                 
                  Site Moderator
                 
                 
                
                
                 •
                
                
                 September 20, 2022


                
                 
                 
                  Pinned Answer

Hi @svenwalrus ,


               
                
                 Make sure your firewall is not the issue. It’s possible you’ve denied outgoing connections on Iptables or UFW (depending on what you use). That’s the first thing I would look.


                
                 
                  sven
                 
                 
                  •
                 
                 
                  September 20, 2022

Solution: Uncommenting #DNS= and #FallbackDNS= and adding Cloudflare IP (1.1.1.1) and Cloudflare fallback (1.0.0.1) in /etc/systemd/resolved.conf resolved the issue for me.


                
                 systemd-analyze cat-config systemd/resolved.conf
before:
# /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=
#FallbackDNS=
#Domains=
#DNSSEC=no
#DNSOverTLS=no
#MulticastDNS=no
#LLMNR=no
#Cache=no-negative
#CacheFromLocalhost=no
#DNSStubListener=yes
#DNSStubListenerExtra=
#ReadEtcHosts=yes
#ResolveUnicastSingleLabel=no
systemd-analyze cat-config systemd/resolved.conf
after:
# /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=1.0.0.1
#Domains=
#DNSSEC=no
#DNSOverTLS=no
#MulticastDNS=no
#LLMNR=no
#Cache=no-negative
#CacheFromLocalhost=no
#DNSStubListener=yes
#DNSStubListenerExtra=
#ReadEtcHosts=yes
#ResolveUnicastSingleLabel=no