Trying to understand what network configuration is doing

[dwasi]

I recently moved a working server to new hardware, and of course the network interface assignments are different. So I used lshw to identify the interface, which called it eno1.

I set this up in /etc/network/interfaces:

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#Production interface
auto eno1
iface eno1 inet static
	address 192.168.1.95
	netmask 255.255.255.0
	gateway 192.168.1.1
	dns-nameservers 192.168.1.1

That surprised me by not working. I poked at it a little bit and ip link show revealed an altname:

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1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eno1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether c4:34:6b:21:2d:44 brd ff:ff:ff:ff:ff:ff
    altname enp3s0f0

So I modified /etc/network/interfaces:

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#Production interface
auto enp3s0f0
iface enp3s0f0 inet static
	address 192.168.1.95
	netmask 255.255.255.0
	gateway 192.168.1.1
	dns-nameservers 192.168.1.1

That worked, but now ifconfig reports both interfaces up; eno1 with ipv6 and enp3s0f0 with ipv4:

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eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 fe80::c634:6bff:fe21:2d44  prefixlen 64  scopeid 0x20<link>
        ether c4:34:6b:21:2d:44  txqueuelen 1000  (Ethernet)
        RX packets 6021587  bytes 3732398704 (3.4 GiB)
        RX errors 0  dropped 42  overruns 0  frame 0
        TX packets 7675170  bytes 7311021949 (6.8 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 17  

enp3s0f0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.95  netmask 255.255.255.0  broadcast 192.168.1.255
        ether c4:34:6b:21:2d:44  txqueuelen 1000  (Ethernet)
        device interrupt 17  

It's not causing me a problem, because I only use ipv4 on the local subnet, but I would like to understand it better. What did I do that resulted in two different interface identifiers for the same interface?

This is Bookworm, if it matters.

[Aki]

Hello,

You may search system logs for network interfaces configuration messages. The following command will let you read system log messages about current boot (root password is required):

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su -l -c "journalctl -b"