How do I get one Dell PowerEdge R720 network interface up?

Andrew Arrow asked:

I have a Dell PowerEdge R720 and it only has one place in the back to plug in a network cable. But it has 5 possible network interfaces:

picture of ip link show

But they are all DOWN when i run ip link show

I’ve tried adding a file in /etc/sysconfig/network-scripts/ for each interface, tried setting the IP manually vs using DHCP, but nothing seems to work.

I run systemctl restart NetworkManager when I make changes and I see in logs:

eno1 state change: unmanaged -> unavailable reason sys-iface-state: external

I know the network cable plugged in works, tried it on another computer. Any ideas what to try next? And how do I know which interface eno1, eno2, eno3, eno4, or enp0s26u1u2u4u4 is the right one?

My answer:

You’ll find the four Ethernet ports on the back directly below the black handle, between the USB ports and the power supply. They are numbered 1-4 and these should correspond exactly to the interface names eno1 through eno4.

The port labeled iDRAC is for out of band management, and this is something you should set up separately.

My best guess about enp0s26u1u2u4u4 is that it’s the iDRAC’s virtual NIC (again, you should set this up separately later).

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