Why would my network interface name change when installing an NVMe?

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nzkc

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#252763 10-Jul-2019 15:46

So I just added a new NVMe card to my motherboard. Previously there was none - just a blank slot.

Booted the box up again and it wouldn't start the interface. Eventually found the interface name had changed from enp6s0 to enp7s0

Why would that be?

My guess is that effectively the network card shifted PCIe ports (from 6 to 7) - is that correct? And I'd then assume that's from adding a new PCIe device in the NVMe.

Its an Ubuntu Server 18.04.2 running KVM so that interface is mapped to a bridge interface (br0...and its this that didnt start cause it was pointing to a now non-existent interface).

Not a biggie as Ive sorted the mapping. Just curious.

wratterus

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#2274105 10-Jul-2019 15:50

Would say that's exactly what's happened.

fe31nz

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#2274379 11-Jul-2019 00:06

I have to chuckle when I see something like this - that change of name is exactly what the new naming system was supposed to prevent. But it doesn't! Unless you have an NVMe card installed, the kernel enumeration skips over the NVMe PCIe lanes and does not leave room for one to be added later.

I personally prefer to have the old (short) ethX names, so I just put a line in my Ubuntu /etc/udev/rules.d/70-persistent-net.rules file for each Ethernet interface:

# Asus P5K-E motherboard
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="00:1f:c6:24:64:ce", NAME="eth0"

# Intel Pro/1000 MT Desktop Ethernet adapter (PCI)
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="00:07:e9:11:c5:95", NAME="eth1"

All you need is the MAC address to put in the "address" attribute, and that can be found in the ifconfig output.

nzkc

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#2274415 11-Jul-2019 08:18

fe31nz:
I have to chuckle when I see something like this - that change of name is exactly what the new naming system was supposed to prevent. But it doesn't! Unless you have an NVMe card installed, the kernel enumeration skips over the NVMe PCIe lanes and does not leave room for one to be added later.

Yeah that's what I thought too (re predictable names). Seems like a great idea with a bit of a flaw!

Certainly wasn't expecting my interface name to change adding a seemingly unrelated component 😀

Add it to the "today I learned" list