Ubuntu Server 20.10: DNS not working

**pelgrim** · April 30th, 2021

I have Ubuntu 20.10 server, with working internet.
pinging addresses work, but DNS not.
I can not update/upgrade ubuntu anymore.
One of the things I need to do with this server is sending out emails.

I spent one day searching on the internet for this, but no solution seems to work for me.

/etc/netplan/50-cloud-init.yaml

Code:

# This is the network config written by 'subiquity'
network:
  ethernets:
    enp5s0:
      dhcp4: true
    enp4s0:
      addresses:
        - 192.168.0.1/24
  version: 2

dig google.com

Code:

; <<>> DiG 9.16.1-Ubuntu <<>> google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 24409
;; flags: qr rd ra; QUERY: 0, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;; Query time: 3 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Fri Apr 30 17:25:30 UTC 2021
;; MSG SIZE  rcvd: 12

dig @8.8.8.8 www.google.com

Code:

; <<>> DiG 9.16.1-Ubuntu <<>> @8.8.8.8 www.google.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42034
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.google.com.			IN	A

;; ANSWER SECTION:
www.google.com.		135	IN	A	172.217.17.68

;; Query time: 11 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Fri Apr 30 17:28:42 UTC 2021
;; MSG SIZE  rcvd: 59

resolvectl query www.google.com

Code:

www.google.com: 142.250.179.196                -- link: enp5s0

-- Information acquired via protocol DNS in 13.6ms.
-- Data is authenticated: no

/etc/resolv.conf

Code:

# ............

nameserver 127.0.0.53
options edns0 trust-ad
search telenet.be

after trying just about anything I get now this result, before Current DNS Server entry was not present.
systemd-resolve --status | grep Current

Code:

      Current Scopes: DNS          
  Current DNS Server: 8.8.8.8      
      Current Scopes: none

appreciate any help.

**TheFu** · April 30th, 2021

Code:

# This is the network config written by 'subiquity'
network:
  version: 2
  renderer: networkd
  ethernets:
    enp5s0:
      dhcp4: false
      dhcp6: false
    enp4s0:
      addresses:
        - 192.168.0.1/24
       dhcp4: false
       dhcp6: false
       gateway4: {your gateway IP}
       nameservers:
         addresses: [ "8.8.8.8", "1.1.1.1" ]

I really think this: 192.168.0.1/24 is incorrect. .1 is almost always the gateway IP. Check that.

Run

Code:

sudo netplan generate
sudo netplan apply --debug

**pelgrim** · May 1st, 2021

TheFu, thank you for your reaction.

enp5s0 is the network to internet
enp5s0:
dhcp4: true

is needed, it goes directly to the internet provider.

everything defined under enp4s0 is not relevant,
this is for the local network, which is out of scope of this question.

This server needs to connect to smtp.gmail.com to send out emails
and needs to find the ubuntu servers for updates, both through enp5s0.
When I replace smtp.gmail.com with an ip address, things work, but that's only a short-term solution.

The lan pc I have connected to enp4s0 is also running ubuntu and has no problems with dns, it can update ubuntu for example without any problem.

**TheFu** · May 1st, 2021

Simplify and test. Get 1 working first.

**pelgrim** · May 2nd, 2021

ok ...
that means you also don't know I assume.

I hope this is picked up by someone.

**TheFu** · May 2nd, 2021

Here, we never have all the facts and have to make reasonable assumptions. For example, I didn't assume this was a router. I assumed it was a server that happened to be connected to multiple networks.

In my post, there is enough to get both NICs working. Just put the gateway and nameservers where they are needed. Also, don't forget to add the renderer. I remember my first 20.04 server install didn't have networking work at all. Seemed fairly odd to me that the installer didn't get 20 lines of simple substitution correct. After the .1 release, I thought it all started working.
I do a few things different than the defaults, like I point directly at my internal DNS and don't run a caching DNS locally. resolvconf and systemd-resolved weren't working for me, and they aren't necessary on LANs with DNS already there. Basically, they are trying to fix a problem that we don't have here ... except when the fix breaks.

**pelgrim** · May 2nd, 2021

hi,

for those that can benefit from it, I finally found something that worked.

Indeed, I should have told that this server also worked as a router.
My mistake.

Now, this is what I performed to get DNS for the server working:

sudo nano etcsystemd/resolved.conf

Code:

DNSStubListener=no

systemctl stop systemd-resolved
sudo rm etc/resolv.conf
echo nameserver 8.8.8.8 | sudo tee /etc/resolv.conf

and bingo, I can
ping www.google.com

**TheFu** · May 2nd, 2021

Ok. Let's look at post #7 above.

The OP is stopping systemd-resolved, so editing the config file has ZERO effect. I think etcsystemd/resolved.conf is a typo. We all make them. I might have made some below:

The correct way to do this is:
Setup a temporary /etc/resolv.conf.new file - and add the lines after the sudoedit command
$ sudoedit /etc/resolv.conf.new

Code:

 nameserver 8.8.8.8
 nameserver 8.8.4.4

If you want more privacy, but fast nameservers, use these:

Code:

 nameserver 1.1.1.1
 nameserver 1.0.0.1

We always want at least 2 DNS servers.

Next, disable systemd-resolved forever. Be certain you "mask" systemd-resolved, so it will work forever.

Code:

sudo systemctl stop systemd-resolved.service
sudo systemctl mask systemd-resolved.service

And quickly, remove the existing /etc/resolv.conf (link/file/whatever) and move the new one into place.

Code:

sudo rm /etc/resolv.conf
sudo  mv  /etc/resolv.conf.new  /etc/resolv.conf

Do this quickly - copy/paste would be best. Sudo may be configured to check which system it is on DNS issues could make it so that sudo doesn't work. We are trying to minimize the chance that the sudo cache expires.

This is probably incorrect:

Code:

sudo nano etcsystemd/resolved.conf

Whenever editing system files, it is safest to use sudoedit for a multitude of reasons. Plus, we can use any editor we like, safely - even GUI editors - if we are on a system that supports GUIs.