mjhjmtu

New to Linux, I have deep problems with my LAN adapter configuration, using Debian 9.5, so I'll describe what's happened then raise my question in hopes that someone can help me.

--First Step:
While installing Debian 9.5, I gave the address I wanted to give to my Lan adapter (no DHCP) : 192.168.58.168 with netmask, network, broadcast and gateway: After installation, I first tried ip a to check the network parameters, and noticed that my LAN adapter was called "ens33":

 2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000
 link/ether 00:0c:29:3a:e1:17 brd ff:ff:ff:ff:ff:ff

 inet 192.168.58.168/24 brd 192.168.58.255 scope global ens33
 valid_lft forever preferred_lft forever

 inet6 fe80::20c:29ff:fe24:2134/64 scope link
 valid_lft forever preferred_lft forever

Then I edited /etc/resolv.conf to add my 2 DNS and after that, the LAN worked perfectly well: I could ping all machines on my LAN and browse the web through Firefox.

Still, the docs I owned told me that the adapters were defined in the file

/etc/network/interfaces

But when I displayed it with cat, I was surprised to notice that the "ens33" interface didn't appear in that file, though I could ping it and though I could see it through ip a . This looked strange to me...

--Second step:
Then after I've added a certain number of packages through apt-get install, including resolvconf and samba, I was satisfied to see that in Dolphin, all the machines of my Windows Domain LAN were visible, and I could even access to the shared directories of my Windows file server and play musical or video files with VLC: Great!

--Third step:
Then I restarted the PC, and nothing works any more: I don't have any LAN access, and if I type ip a to see my LAN definitions, I can see that the "ens33" adapter has lost its properties:

ens33: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
 link/ether 00:0c:29:3a:e1:17 brd ff:ff:ff:ff:ff:ff

So I added the ens33 section to the file
/etc/network/interfaces

Now this file is as follows:

'# The loopback network interface
auto lo
iface lo inet loopback
auto ens33
iface ens33 inet static
 address 192.168.58.168
 netmask 255.255.255.0
 network 192.168.58.0
 broadcast 192.168.58.255
 gateway 192.168.58.11
iface dns-nameservers 192.168.58.11 192.168.58.21

As you can see, resolvconf added the 2 DNS I had defined in the file

/etc/resolvconf/resolv.conf.d/base

because when I added them in the resolv.conf file, they were automatically erased since I had installed resolvconf...

But it didn't solve the problem, even after reboot: So, I tried:

ifup ens33

But the system answered:

ifup: /etc/network/interfaces:16: unknown or no address type and no inherits keyword specified
ifup: couldn't read interfaces file "/etc/network/interfaces"

This "couldn't read interfaces file" is quite incomprehensible to me, because if I type:

cat /etc/network/interfaces

it displays just what I reported above.

So, it seems that the "interfaces" file has no real power because:

1: In the beginning, ens33 didn't appear in that file, and still the network was fully operational

2: When I add the interface's definitions in that file, it has no effect on the machine

So I would like to know: Which damn Linux file(s) really fundamentally define(s) the LAN adapter's parameters ???

Thank you to help a poor man turning mad with that stuff!