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I'm running Ubuntu 21.04 with Network Manager disabled because it doesn't support some of the features required by Wi-Fi 6E. I'm performing the manual configuration based on this article.

When starting the system, the network interfaces do not obtain an IPv4 address with DHCP. The system has two interface, enp0s31f6 and wlp2s0, which are Ethernet and Wi-Fi respectively.

/etc/network/interfaces looks like this:

$ cat /etc/network/interfaces
auto lo
iface lo inet loopback

auto enp0s31f6
iface enp0s31f6 inet dhcp

auto wlp2s0
iface wlp2s0 inet dhcp

With this file, neither interface obtains an IPv4 address with DHCP.

However if I issue these terminal commands

sudo dhclient enp0s31f6
sudo dhclient wlp2s0

the interfaces will obtain addresses from DHCP and operate normally (until the next restart)

Why is the /etc/network/interfaces file not causing this to happen when the system starts?

tim11g
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  • The linked article looks rather old - it doesn't even mention `netplan` for example. When you disabled NetworkManager, did you configure `netplan` to use an alternate renderer? See for example [netplan vs NetworkManager on Ubuntu 18.04 and above](https://askubuntu.com/questions/1122757/netplan-vs-networkmanager-on-ubuntu-18-04-and-above) – steeldriver Jul 07 '21 at 01:48

1 Answers1

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I think is the same reason as debian. NetworkManager does not manage any interface defined in /etc/network/interfaces by default.

Unmanaged devices means NetworkManager doesn't handle those network devices.

https://wiki.debian.org//NetworkManager#Wired_Networks_are_Unmanaged

leave just lo interface in that file:

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