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I use Ubuntu 16.04 and connect my machine alongside other machines by using a Hub to a modem to use Internet. Today I encounter with a problem:

Other machine can connect to the Internet; but I cannot access web (Server Not Found error on browser and ping: unknown host google.com as result of $ ping google.com in terminal), unless after doing disconnecting/re-connecting network cable. But this way only works for a few seconds up to 2 minutes. Although my Android device can connect to the web continuously without any problem through WiFi.

Also I connected my machine directly to the modem and even changed the network (Ethernet) cable. But result was the same.

What causes this problem and how I can solve that?

Edit1

I can open 192.168.1.1 from my machine but cannot login; although it is possible to do that from my other machines.

Edit2

  • /ect/resolv.conf only contains nameserver 127.0.1.1 (but that file is a link to /run/resolvconf/resolv.conf)
  • the result of $ nmcli device show $ethernet | grep DNS is:
    • IP4.DNS1: 8.8.8.8
    • IP4.DNS2: 4.4.4.4 -ping 8.8.8.8 works always
  • Both $ dig 8.8.8.8 google.com and $ dig 4.4.4.4 google.com work when I can access web ; but when problem occurs, I get ";; connection timed out; no servers could be reached"

Edit3

It seems that my machine automatically changes used connection from Internet (which is used to access web) to virbr0 which causes problem:

When I can access web: enter image description here

When problem occurs: enter image description here

Edit4

Result of $ ip route show when I can access & cannot access the web:

default via 192.168.1.1 dev eno1  proto static  metric 100 
169.254.0.0/16 dev eno1  scope link  metric 1000 
192.168.1.0/24 dev eno1  proto kernel  scope link  src 192.168.1.50  metric 100 
192.168.122.0/24 dev virbr0  proto kernel  scope link  src 192.168.122.1 linkdown 
  • You can connect to the router but not login, yet you can on other PC's? Curious, I would be looking for a second router, that could explain all of your issues. – acejavelin Aug 3 '18 at 11:02
  • What is the virtual bridge for? – xenoid Aug 3 '18 at 20:04
  • Next step is doing ip route show in both cases. – xenoid Aug 3 '18 at 20:26
  • @xenoid I think virbr0 must be created and used by VirtualBox. – hasanghaforian Aug 4 '18 at 1:40
  • @xenoid Result of $ ip route show in both cases are same. I added result to my question. – hasanghaforian Aug 4 '18 at 1:54
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Likely a DNS problem..

  • check that your /ect/resolv.conf only contains nameserver 127.0.1.1,
  • issue nmcli device show $ethernet | grep DNS to list the nameservers ($ethernet is the name of your interface, normally some enp*)
  • check if you can access these (ping...)
  • check if they can be used dig @dnserver somesite.com

The connection editor lets you to force a DNS in your connection, for instance:

  • 8.8.8.8 (Google)
  • 208.67.220.220/208.67.222.222 (OpenDNS)
  • Thank you for your reply. I updated my question, please see it again. Also it seems you are sure that the problem is not in about hardwares, for example network card. Did I guess true? – hasanghaforian Aug 3 '18 at 10:34
  • Since it works when you disconnect/reconnect then no too likely tthe hardware. Does disconnecting/reconnecting Ethernet using the systray applet also fixes (temporarily) the problem? Otherwise, look in /var/log/syslog around the time you loose the DNS resolution. Also, does it work if you connect to a totally different network (or not using the hub) ? Is everything in DHCP without any possibilty that two machines get the same IP address? – xenoid Aug 3 '18 at 11:56
  • I checked my connection and /var/log/syslog. Now I edited my question please see it again. – hasanghaforian Aug 3 '18 at 18:37

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