Troubleshooting networking issues after fresh install of proxmox VE 4.4

Writing a quick troubleshooting guide and informative post to address an issue I came across when installing Proxmox VE 4.4 on two of my machines.

On servers with more than two network interfaces Debian/Proxmox renames all interfaces and does not properly detect eth0 as the on-board ethernet as many other linux flavors. This may cause a mild headache if you just installed Proxmox with static IP addresses using the installer and upon reboot you can’t access any network resources.

I already explained the cause and you could argue that on the Proxmox installer they could add a built-in network detection check to properly label eth0 as eth0 as the device is named in many other linux distros. That currently does not exist so I will walk you around the troubleshooting.

Upon reboot or first boot after the installation is complete:
# ip link

The bridge interface (vmbr0) should read “NO-CARRIER, MULTICAST, UP” as well as “state down” a few words further to the left of the results.

# dmesg | grep eth

Read the entries in the dmesg logs, it tells you the name of network interfaces on your system.

NO-CARRIER” indicates it does not detect an uplink, the interface is configured but none of its bridge members have a network cable or connection being detected.

To fix this you will want to run the following commands:
# ifdown -a
# vi /etc/network/interfaces

By default the installer sets up “eth0” as your only bridge member since the network card numbering got setup differently, the logical name on proxmox for eth0 is actually eth2.

Edit the single instance of eth0 with eth2 – save the file and exit the editor.

# ifup -a
should try to bring back up your interfaces. Trying pinging your network gateway, it should be working now. Cheers.

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