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

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

I tried connecting 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 it?

Edit

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

Edit1

I checked my connection and /var/log/syslog. 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

I think virbr0 must be created and used by VirtualBox. I use VirtualBox 5.1.38. Also sometimes I can access the web without any problem from my guest OS, during time that I cannot do that from host! But I created guests along time ago, for example 2 or 3 monthes ago, and this problem occurred only this week.

Edit2

result of nslookup askubuntu.com when I can access the web:

$ nslookup askubuntu.com
Server:     127.0.1.1
Address:    127.0.1.1#53

Non-authoritative answer:
Name:   askubuntu.com
Address: 151.101.1.69
Name:   askubuntu.com
Address: 151.101.65.69
Name:   askubuntu.com
Address: 151.101.129.69
Name:   askubuntu.com
Address: 151.101.193.69

Edit3

I did these; but problem remains:

  • using another modem
  • replacing network cable with another

Also I tethered my machine to an Android device and could access the web without any problem.

Edit4

I could connect to Internet in guest session without any problem, so it seems that problem only occurs on my current account and I'm sure NIC does not cause this problem.

  • This sounds to me like a dodgy connection. It could be the cable, but if you've replaced that with a tested known good cable it could also be caused by a bad ethernet port on your system. I'vwe seen bent pins occasionally on these ports interfere with proper connectivity to ANY cable.. – Elder Geek Aug 4 '18 at 17:05
  • @ElderGeek I edited my question, please see it again. – hasanghaforian Aug 5 '18 at 9:34
  • You are likely correct in your assumption that virbr0 is created and used by your VM software. It's typically a virtual bridge interface. I've never had it interfere with host network access though, so that is odd. The problem provides the clues however. Are you certain that you are using a hub and not a switch? I honestly haven't seen a hub in use on a network in over a decade due to speed concerns and the excessive traffic that they produce as packets are flooded out every port as the MAC addresses attached to the ports are unknown. – Elder Geek Aug 5 '18 at 14:53
  • @ElderGeek It seems I connect machines to a switch; but I think it does not cause that problem. Because as I mentioned in my question, I connected my machine directly to the modem (without using a switch) and problem occurred again. – hasanghaforian Aug 6 '18 at 1:53
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    I'm voting to close this question as off-topic because I am convinced that this is a hardware problem. – Elder Geek Aug 6 '18 at 16:57
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The fact that your problem is intermittent indicates to me a very few possibilities when taking into consideration all the facts as you have presented them. The switch isn't the problem as bypassing it doesn't resolve the issue.

1) Intermittent short in the Ethernet cable. Replace with new cable.

2) Failing NIC. (specifically the Ethernet port). Replace NIC

3) Failing modem (specifically the Ethernet port). Replace modem or obtain a cheap WiFi adaptor and use that to connect since Wifi is stable.

All of these possible solutions are extremely cost effective.

Edit: If you determine that your problem is not hardware related and think that it's caused by something ill advised you did to your profile due to other accounts working properly you can confirm whether this is indeed the case by repairing your profile.

  • Thank you again for your times and replies. I did some works and edit my question. Probably NIC causes the problem. – hasanghaforian Aug 7 '18 at 9:28
  • I can access the web in guest session without any problem. So I'm sure NIC does not causes the problem. – hasanghaforian Aug 7 '18 at 14:31
  • @hasanghaforian edited answer – Elder Geek Aug 8 '18 at 21:16

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