There is no single reason why you should disable IPv6 in your Ubuntu server, nor it must. It depends on your requirement. It has been reported for a while that IPv6 in Ubuntu cause DNS related problems. For example, the apt package manager occasionally tries to initiate the connection over IPv6 and fails.
Sep 29, 2019 How to use the same DNS for all connections in Ubuntu (and Apr 28, 2020 Domain Name Service (DNS) - Ubuntu Domain Name Service (DNS) Domain Name Service (DNS) is an Internet service that maps IP addresses and fully qualified domain names (FQDN) to one another. In this way, DNS alleviates the need to remember IP addresses. Computers that run DNS are called name servers. Ubuntu ships with BIND (Berkley Internet Naming Daemon), the most common program
Install Netplan on Ubuntu – Linux Hint
I'm having issues with DNS lookups on my new install running Ubuntu 18.04 LTS. It uses the Linode "Auto-configure Networking" and I haven't made any changes to network config files. The problem: emails weren't being sent because lookups don't resolve. How to Flush DNS Cache in Linux in 2020 [Guide] | Beebom
Resolving domains on Ubuntu is not working 16.04.4 LTS. The home server is connected to the Huawei HG8245 router, the network on the server is parsed by NetworkManager. The NetworkNamager configuration includes dnsmasq (dns = dnsmasq). NetworkManager works.
This issue can be related to systemd-resolve does not forward DNS requests to stated DNS server. Newer systemd-resolved refuses to resolve simple names via DNS, i.e. myhost and will only resolve myhost.somedomain.com via DNS. This change is by design. Bypass/remove systemd-resolved if you use simple hostnames. Flush DNS Cache on Ubuntu – Linux Hint On Ubuntu 16.04 LTS, DNS cache is not enabled by default. But some applications like bind, dnsmasq, nscd etc. may cache it. If you’re using nscd for caching DNS queries, then you can flush the DNS cache by simply restarting the nscd service. You can restart the nscd service on Ubuntu 16.04 LTS to flush DNS caches with the following command: [SOLVED] How to no connectivity Ubuntu DNS problem [fix] Apr 19, 2017 Fixing DNS Issues in Ubuntu 18.04 LTS | by Ahmad Bilal