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Recently I did the usual update + upgrade .. however after doing so, my network interface refused to work. ( no connection )

What happened ? How can I get bring my network-interface up ? ... I am running a debian - stretch.

( The same issue might occur on debian-derivates, like e.g. Ubuntu)

3 Answers 3

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After some search in the web ( god sake I have as well a laptop ) I figured out that some renaming of the network interfaces occurred ... so first thing to do: See which network interfaces currently are up ( for me only the Loopback was started )

sudo ifconfig

Now let's check the naming of all available network interfaces:

networkctl

For me the output looked like that:

WARNING: systemd-networkd is not running, output will be incomplete.

IDX LINK             TYPE               OPERATIONAL SETUP     
  1 lo               loopback           n/a         unmanaged 
  2 enp3s0           ether              n/a         unmanaged 
  3 enp4s0           ether              n/a         unmanaged

After that I took a look into /etc/network/interfaces ... which for me looks like that:

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# Comment in the right one (the one plugged in) otherwise system.d will run a startjob
#auto net0
#allow-hotplug net0
#iface net0 inet dhcp

auto net1
allow-hotplug net1
iface net1 inet dhcp

... you probably can guess what comes next ... replace net0 / net1 (or whatever you have there) by the LINKS listed by networkctl.

Start the new interface (or reboot):

sudo ifup enp3s0

And check if it is listed now:

sudo ifconfig
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  • 1
    Thanks! I just had the same issue. Seems that with my 'i386' install I can add a network card with no problem, but with the latest stretch/sid/amd64, when I add a card, the internet stops working until I made the modification above. Seems good old 'eth0' no longer works. Dec 21, 2016 at 18:11
  • You saved me hours of googling. Thanks man, I used to configure linux interfaces a while back but a lot of things changed.
    – Diego
    May 23, 2020 at 15:01
  • Had a problem where an interface coming from the Ethernet port on the motherboard got an inet address automatically, but the interface from a Ethernet->USB adapter was "DOWN" at boot (I'd need to ip link dev [ifacename] up manually each time). Surely enough, the USB iface was not in /etc/network/interfaces and I needed to add it manually. Thanks! Mar 6, 2021 at 23:56
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I had this situation too. What helped for me:

If this is under Hyper-V and the network interface stops immediately after system boot/start: then the reason is irqbalance.service. This service should be disabled.

Symptoms:

  • ping from other machine: upon reboot you will observe a few succesful pings and than nothing (unreachable)
  • in /var/log/syslog you will see lines with something like: kernel: [ 2758.780340] net eth1: 21140 transmit timed out, status fc6981c7, SIA fffffe00 00000068 00000070 fffffec8, resetting...
  • arp will show incomplete hw address for your default gateway etc.

Solution (choose one):

  1. disable via systemctl disable irqbalance.service and then reboot
  2. edit the /etc/default/irqbalance to disable the service and then reboot

Please note that in 99% of situations you will NOT need the irqbalance.service under Hyper-V. It is useless unless under very specific configuration.

My configuration: Hyper-V machine with Debian Jessie (upgraded from Wheezy) and immediately after upgrade: networking stopped (no ping etc). Googled very long for an answer until found.

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I had similar problem (debian stretch, realtek network card). My network card hadn't received IP addr from DHCP server. Try command dhclient to get IP addr from DHCP server. If it helps, check contenets of the /etc/network/interfaces file. In my system files from folder interfaces.d were ignored (despite it was pointed in interfaces file). I simply copied contents of ./interfaces.d/realtek file to the interfaces.

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