CentOS 7 : Network Interface Renamed From Eth0 To Eth1 After Reboot

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Hi,

I’ve done my fair share of CentOS 7 installations, but this is the first time I
have this kind of weird problem. Here goes.

In my office I have a battered Dell Optiplex 320 PC with two NICs that I’m using as a bare metal sandbox server for testing purposes.

The CentOS 7 installer sees the connected network card as eth0. But after the first reboot, the interface comes up as eth1.

My first reflex was to rename ifcfg-eth0 to ifcfg-eth1 and edit it accordingly. Weirdly enough, on the subsequent reboot the interface comes back as eth0.

I took a peek in /etc/udev/rules.d to see if there was any persistent interface definition, but the directory is empty.

On a side note, I installed Ubuntu Server 16.04 LTS on that same machine and got the exact same problem. Debian installer sees the main network interface as eth0, but on the first reboot the interface comes back as eth1.

Any suggestions ?

Niki

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11 thoughts on - CentOS 7 : Network Interface Renamed From Eth0 To Eth1 After Reboot

  • Le 09/02/2020 à 14:52, Salim Shaw a écrit :

    There is no wireless device on this PC.

    Just an onboard NIC and then an additional PCI NIC.

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  • Hello, Am Sonntag, 9. Februar 2020, 14:10:44 CET schrieb Nicolas Kovacs:

    this is coming from The NetworkManager?

    I set in my config *-eth0 the HWADDR=XXXXXXXXXXXX
    and NM_CONTROLLED=no

  • Le 09/02/2020 à 15:15, Günther J. Niederwimmer a écrit :

    I forgot to add : I removed NetworkManager as I do on all my servers.

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  • Le 09/02/2020 à 14:10, Nicolas Kovacs a écrit :

    I forgot to add. The onboard NIC is a Broadcom card.

    $ lspci | grep -i net
    02:02.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8100/8101L/8139 PCI Fast Ethernet Adapter (rev 10)
    02:09.0 Ethernet controller: Broadcom Inc. and subsidiaries BCM4401-B0
    100Base-TX (rev 02)

    This card gets randomly renamed to either eth0 or eth1 after every reboot.

    This is weird.

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  • Le 09/02/2020 à 16:54, Alexander Dalloz a écrit :

    Thanks for the heads up.

    I experimented quite a bit, and found some surprising behavior. So I documented everything in a little blog article.

    * https://www.microlinux.fr/interfaces-reseau-persistantes/

    Cheers,

    Niki

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  • So yeah if there are certain cards, certain bios firmware, the eth? are not guarenteed. The upstream kernel will say it is not a bug as everything is doing what it is doing, and will point out various things where eth? is really an internal kernel representation which is only accurate by luck. What you are supposed to do is rename the interface (I think the docs I
    found said net0 or whatever you want) and link the two via udev or similar rules. That way the udev sets up and sees ‘this pci/network is blah.. alias it to net0 and pass that so the scripts work. Then network-scripts or networkmanager or whatever sets up and down net0 versus a ‘semi-random’ eth interface. [For kernels beyond 4.?? and beyond I am expecting that this will be a more stringent requirement]

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  • There may be ways to force NIC naming, I’ve done so but only on Ubuntu so you’ll need to do the research if it’s important to you. Things to look for based on my experience: 70-persistent-net.rules, net.ifnames=0, biosdevname=0.

  • I cheated; I use NIC teaming, and before starting networking, run a script that iterates over NICs, picking up their current device names, and scripting the if-cfg* files.

    I had to do this when a few years ago, Dell was getting clever about renaming NICs aggressively, and nothing could trust ‘eth0’ anymore. Now, I always get a ‘bond0’.

    (Oh, and I also disabled NetworkManager, because, like systemd, it tries to be Too Clever for it’s own good.)

    Overkill for most, I admit, but it make my installation media much more portable.

  • Le 10/02/2020 à 16:12, Leroy Tennison a écrit :

    That’s exactly the solution I described in detail in my blog article.

    :o)

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