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Hi all i have been running Ubuntu Server 16.04 on my headless server for several months without issue, recently i took the server offline for some routine cleaning & replaced a PSU, upon booting it back up for some reason the server has no outgoing internet connection here are the results of some tests

ben@ubuntu:~$ ping -c5 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=55 time=23.7 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=55 time=23.5 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=55 time=23.6 ms
64 bytes from 8.8.8.8: icmp_seq=4 ttl=55 time=23.3 ms
64 bytes from 8.8.8.8: icmp_seq=5 ttl=55 time=29.9 ms

--- 8.8.8.8 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4006ms
rtt min/avg/max/mdev = 23.396/24.844/29.937/2.556 ms

trying to ping a hostname

ben@ubuntu:~$ ping www.cisco.com -c 1 -s 1472 -M do
ping: unknown host www.cisco.com
ben@ubuntu:~$

Ping www.cisco.com via IP adress

ben@ubuntu:~$ ping -c5 23.204.15.199
PING 23.204.15.199 (23.204.15.199) 56(84) bytes of data.
64 bytes from 23.204.15.199: icmp_seq=1 ttl=46 time=229 ms
64 bytes from 23.204.15.199: icmp_seq=2 ttl=46 time=229 ms
64 bytes from 23.204.15.199: icmp_seq=3 ttl=46 time=239 ms
64 bytes from 23.204.15.199: icmp_seq=4 ttl=46 time=229 ms
64 bytes from 23.204.15.199: icmp_seq=5 ttl=46 time=229 ms

contents of resolv.conf

# This file is managed by man:systemd-resolved(8). Do not edit.
#
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.
nameserver 127.0.0.53

contents of if config

ben@ubuntu:~$ ifconfig
enp8s0    Link encap:Ethernet  HWaddr 00:1e:67:51:8e:8c
          inet addr:192.168.0.251  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::21e:67ff:fe51:8e8c/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1492  Metric:1
          RX packets:20820 errors:0 dropped:50 overruns:0 frame:0
          TX packets:16017 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:4243433 (4.2 MB)  TX bytes:4596251 (4.5 MB)
          Interrupt:16 Memory:c2300000-c2320000

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:18434 errors:0 dropped:0 overruns:0 frame:0
          TX packets:18434 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1
          RX bytes:2225861 (2.2 MB)  TX bytes:2225861 (2.2 MB)

contents of /etc/network/interfaces

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto enp8s0
iface enp8s0 inet static
address 192.168.0.251
netmask 255.255.255.0
gateway 192.168.0.1
dns-nameservers 8.8.8.8 8.8.4.4

contents of /etc/hosts

127.0.0.1       localhost
127.0.1.1       ubuntu

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

I can SSH into the box from my mobile phone using 4G connection (outside of my local network)

Any ideas, system has been running great now all of a sudden no internet access,

Thank You

-Ben

gimpacause
  • 41
  • I wonder if the dnsmasq service is not working? Did you try what it says in the resolve.conf file to run systemd-resolve --status? If you want, you can turn off dnsmasq by commenting out the dns=dnsmasq line in the /etc/NetworkManager/NetworkManager.conf file then restart. That is what I have done on my system and found I have less issues. – Terrance Nov 19 '17 at 04:31
  • Hi Terrance, I tried "systemd-resolve --status"

    below is the outcome

    systemd-resolve: unrecognized option '--status'

     – gimpacause Nov 19 '17 at 06:27
  • Yeah, that command didn't work for me either, I only suggested it because the resolve.conf was suggesting that you run it. But, did you try the other part of my suggestion so that DNS is not handled by your computer and handled by the DHCP / DNS server? – Terrance Nov 19 '17 at 06:35
  • ok just checked i my /etc/NetworkManager/NetworkManager.conf is empty, can't seem to see why a PSU swap would mess with the network config – gimpacause Nov 19 '17 at 08:20
  • I am with you on this one. It is very strange. With you being able to ping IP addresses of websites, but not being able to ping them by name, to me that shows DNS not working. Why it started after you replaced a power supply, I have absolutely no idea. It could be that you're missing the NetworkManager.conf file. I will write it up in an answer really quick and you can try it. – Terrance Nov 19 '17 at 22:36
  • I just had an idea. Run the command grep 127.0.0.53 /etc/resolvconf/resolv.conf.d/* and see if there is any output. There might be a chance that if we set proper DNS in /etc/resolvconf/resolv.conf.d/original that it might fix your DNS problem. – Terrance Dec 11 '17 at 16:56
  • Hi @Terrance I have tried the above suggestion and this is what i get

    [code]

    ben@ubuntu:~$ grep 127.0.0.53 /etc/resolvconf/resolv.conf.d/* grep: /etc/resolvconf/resolv.conf.d/*: No such file or directory ben@ubuntu:~$

    [/code]

    Thank you

     – gimpacause Dec 17 '17 at 09:20
  • OK, maybe we need to try disabling systemd-resolved as none of my systems are using it and they seem to be holding DNS pretty well. Have a look at https://askubuntu.com/questions/907246/how-to-disable-systemd-resolved-in-ubuntu – Terrance Dec 18 '17 at 14:17
  • Hi Terrance, Hope your holidays are going good

    browsing around google i came across a page describing an issue similar to mine and tried the fix there i entered the command sudo dhclient enp8s0 and i regained internet access, what file should i look at see what went wrong, thank you for your help so far

     – gimpacause Dec 30 '17 at 12:00
  • Yeah, the holidays are good. Interesting, you have your nic set for static and not dhcp, so I would have not thought that would have made any difference. Maybe setting your nic to DHCP in the/etc/network/interfaces file and giving it a reserved IP in your router. Or you might need to give that system a reserved IP in the router regardless so that the router doesn't try to give out that IP to another system. That could have happened. – Terrance Dec 31 '17 at 21:09

0 Answers0