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Accepted
lewis4u
Asked: 2019-06-14 00:38:27 +0800 CST

Why does static IP in Ubuntu 16 work only like this?

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We have a windows server with DHCP and 2 Linux machines with Ubuntu 16

if we set /etc/network/interfaces like this:

# The loopback network interface
auto lo eth0
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
address 192.168.1.18
netmask 255.255.255.0

allow-hotplug eth0
  iface eth0 inet dhcp

Then all works fine. So in short, first the machine sets static IP then it uses DHCP and it gets that ip 192.168.1.18

And if we delete those two last lines:

allow-hotplug eth0
  iface eth0 inet dhcp

There is no internet at all on the machine. Can anyone explain this please?

networking server dhcp

1 Answers

  1. Best Answer

    "Can anyone explain this please?" Yes, your interfaces file is seriously deficient. You have not specified a gateway nor the very important DNS nameservers.

    I suggest that you amend the file to:

    # The loopback network interface
auto lo eth0
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
address 192.168.1.18
netmask 255.255.255.0
gateway 192.168.1.1
dns-nameservers 8.8.8.8 192.168.1.1

allow-hotplug eth0

    Please be certain that the specified static IP address is outside the DHCP range in the router to avoid collisions.

    Restart the interface:

    sudo ifdown eth0 && sudo ifup -v eth0

    Confirm that you are connected:

    ping -c3 www.ubuntu.com
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