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====== Renaming network interfaces ======

===== With Debian 10 Buster =====

How to rename a network interface from e.g. **enx00e04c885302** to something more human like **lan0**? The preferred method is to create a file **/etc/systemd/network/10-persistent-lan0.link** (one file for each interface to be renamed) with something like this:

<file>
#/etc/systemd/network/10-persistent-lan0.link
[Match]
MACAddress=00:e0:4c:88:53:02
[Link]
Name=lan0
</file>

**WARNING**: You cannot use this method to safely assign the default kernel names (''eth0'', ''eth1'', ...) in your preferred order; this is because if systemd tries to rename an interface using a name which is already assigned by the kernel (e.g. it tries to swap ''eth0'' and ''eth1''), it fails. So the target **Name** must not potentially conflict with the names assigned by the kernel.

**WARNING**: This method has an additional problem if you need to create a **VLAN**. When the system creates e.g. the **lan.602**, its MAC address matches the systemd snippet, so systemd tries to assign to it the name (**lan0** in the example above) but the name already exists, so the interface remains with a temporary name e.g. **rename5**.

A workaround can be the following: tell the kernel to use the old ''ethX'' schema (passing the **net.ifnames=0** option), then instruct systemd to act only on **%%eth*%%** network interfaces:

<file>
[Match]
MACAddress=00:e0:4c:88:53:02
OriginalName=eth*
[Link]
Name=lan0
</file>

==== NetworkManager interfering with rename ====

Both methods seen above seem to work, unfortunately on my XFCE environment, the **NetworkManager** stepped into the play, reverting back the name:

<file>
NetworkManager[581]: <info>  [1620916630.3558] device (eth0):
   interface index 10 renamed iface from 'eth0' to 'enx00e04c885302'
</file>

If you want to **manage the interface using NetworkManager** from the user session, be sure that the interface is not referred by **/etc/network/interfaces** or any snippet file into ''/etc/network/interfaces.d/''. If the interface is configured by ''/etc/network/interfaces'', NetworkManger will ignore it, labelling as //unmanaged//.

==== Use the old naming schema (eth0, ...) ====

If you want to use the old naming schema (eth0, eth1, ...) enable the kernel override option in **/etc/default/grub**:

<file>
GRUB_CMDLINE_LINUX="net.ifnames=0 biosdevname=0"
</file>

Followed by **update-grub** and **reboot**.

Beware that by using that schema the card's assigned name depends upon the time when the kernel discover the interfaces, in some cases you may find the names swapped after a reboot, even if the Ethernet cards are fixed built-in.

===== How it worked in the old days of Debian 4 Etch =====

In a modern Linux system, network interface drivers are compiled as modules. Generally there is a subsytem that provides loading kernel modules automatically. Debian GNU/Linux Etch uses ''**udev**'' for that.

Interface names (eth0, eth1, ...) are assigned as they are discovered and kernel modules are loaded, unfortunately the order of discovering can sligtly vary across reboots. So you can find that after a reboot your system has swapped **eth0** and **eth1**, with all the nasty consequences you can imagine.

I suggest two ways to assign interface names in a consisten way.


==== udev ====

In a Debian Etch box, check the **''/etc/udev/rules.d/z25_persistent-net.rules''**. This file is updated at bootstrap when new network interfaces are found. It contains a persistent mapping of MAC addresses to interface names.

In general, add a custom configuration file ''**/etc/udev/rules.d/010_netinterfaces.rules**'' with lines like this:

<file>
KERNEL=="eth*", SYSFS{address}=="00:12:34:fe:dc:ba", NAME="eth0"
</file>

In the above example we used the SYSFS{address} as a match for the rule, use this command to print all sysfs properties of the specified device that can be used in udev rules to match the specified device:

<code>
udevinfo -a -p /sys/class/net/eth0
</code>

==== ifrename ====

You configure this userspace program writing the configuration file''**/etc/iftab**'':

<file>
# Example /etc/iftab file
eth2           mac 08:00:09:DE:82:0E
eth3           driver wavelan interrupt 15 baseaddress 0x390
eth4           driver pcnet32 businfo 0000:02:05.0
# wildcard name: pick the lowest available name of air0, air1, air2, etc.
air*           mac 00:07:0E:* arp 1
</file>

The good thing of this program is that you can select intefaces by the name of the kernel module, by MAC address, by bus position and other methods. But beware that the standard Debian startup of ''ifrename'' runs the program once, **when all the interfaces are already discovered and named**. In this case **it is not possible to swap two interface names**, because when you try to rename the first interface, an error occurr: ''Error: cannot change name of eth1 to eth0: File exists''.

===== Debian 8 Jessie =====

The udev cache file is named now **''/etc/udev/rules.d/70-persistent-net.rules''**, sometimes only one Ethernet card is automatically added to this file, some other times the cache file is not created at all.

To force the creation of that file just execute the command:

<code>
udevadm trigger --action=add
</code>

===== Debian 9 predictable network interface names =====

Esempio: **enp3s0f1**

  * **en** Ethernet network card
  * **p3** PCI bus #3
  * **s0** Slot #0
  * **f1** Function #1 (eg. a dual porta LAN has two //functions//).

Per disabilitare questa funzione, chiamata **[[https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/|Predictable Network Interface Names]]** è possibile aggiungere l'opzione kernel **net.ifnames=0** ad esempio in ''/etc/default/grub'', opzione **GRUB_CMDLINE_LINUX**.

Se è installato la //helper utility// di udev chiamata **biosdevname**, è opportuno passare al kernel anche il parametro **biosdevname=0**.

Avendo attivato l'opzione **net.ifnames=0** può essere comunque desiderabile una persistenza nell'assegnare il nome all'interfaccia , considerato che il kernel assegna i nomi legacy **eth0**, **eth1**, etc. in base all'ordine di rilevamento hardware, che è non deterministrico. È possibile quindi creare un file **/etc/udev/rules.d/70-network.rules** con l'assegnamento statico in base al MAC address, ad esempio

<file>
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="00:30:67:9a:75:0b", NAME="eth0"
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="00:18:e7:22:0b:f7", NAME="eth1"
</file>

:!: **ATTENZIONE**: Pare che **il file con le regole udev viene ignorato** se manca l'opzione **net.ifnames=0** nella cmdline del kernel! Questo almeno è accaduto con Debian 11.7 e kernel 5.10.0-23-amd64.

:!: **ATTENZIONE**: Il file con le regole udev viene ignorato comunque in **Debian 11**.

===== Debian 9 Network Interface Naming =====

  * **[[http://metadata.ftp-master.debian.org/changelogs/main/s/systemd/systemd_221-1+deb9u2_udev.README.Debian|udev Debian README]]** (local copy [[udev_readme_debian|here]]).
  * **[[https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/|Predictable Network Interface Names]]**