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My setup: I have 2 virtual box machines that run CentOS, Server1 and Server2.

Server1 is configured with 2 network interfaces which are enp0s3 and enp0s8. enp0s3 is connected to VM NAT network with network ID 10.0.2.0 and enp0s8 is connected manually to network with id 192.168.1.0.

Server2 has only 1 interface which is enp0s3 and is on the same network as server1's enp0s8 (192.168.1.0). So server one is host 1 and server2 is host 2 (192.168.1.1, 192.168.1.2).

The problem: While on server1, I tried to ping google.com to see if I have network connectivity. It didn't work. Therefore, I took the following step in order to troubleshoot it.

1) I did ping -I enp0s3 (to ping with NAT connected interface), and it didn't work

2) I did ping 8.8.8.8 and it worked! so I thought this is some DNS problems

3) And since I don't know anything about DNS yet, I went in to /etc/resolv.conf and changed the nameserver to google public DNS server. It worked, so ping google.com works now!

4) I could leave it like that but I wanted to narrow down the source of the problem so I went ahead and reverted the change in /etc/resolv.conf back to 192.168.1.1

5) I asked myself, why my DNS server is on a private network which is not even connected to the outside world. At that point, I went and checked my host machine's IP address, and it was 192.168.1.1

6) After discovering that my host machine has same network id as my private network in Virtual box I thought that it may cause some conflicts so I went and changed private network id to 192.168.3.0 and that solved everything.

But... The question I still have what exactly causes this problem.

mazaneicha
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Anton Stafeyev
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  • If using DNS 8.8.8.8 worked and using an internal one didn't it's logical to assume that there's something wrong with your internal DNS or it's connectivity to the outside. – Overmind Jul 09 '19 at 12:57
  • @Overmind yeah but once i disable enp0s8 it works, and it works when i change the network on esp0s8 so it has nothing to do with internal dns because it works on this circumstances – Anton Stafeyev Jul 09 '19 at 13:50
  • @Overmind please read the question carefully – Anton Stafeyev Jul 09 '19 at 13:50
  • If it works when you disable an interface and no longer works when you enable it back, it means it's a routing AD priority problem. – Overmind Jul 10 '19 at 12:25

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