Chapter 11. Consistent Network Device Naming
Chapter 11. Consistent Network Device Naming Red Hat Enterprise Linux provides methods for consistent and predictable network device naming for network interfaces. These features change the name of network interfaces on a system in order to make locating and differentiating the interfaces easier. Traditionally, network interfaces in Linux are enumerated as eth[0123...]s0 , but these names do not necessarily correspond to actual labels on the chassis. Modern server platforms with multiple network adapters can encounter non-deterministic and counter-intuitive naming of these interfaces. This affects both network adapters embedded on the motherboard ( Lan-on-Motherboard , or LOM ) and add-in (single and multiport) adapters. In Red Hat Enterprise Linux, udev supports a number of different naming schemes. The default is to assign fixed names based on firmware, topology, and location information. This has the advantage that the names are fully automatic, fully predictable, that they stay fixed even if hardware is added or removed (no re-enumeration takes place), and that broken hardware can be replaced seamlessly. The disadvantage is that they are sometimes harder to read than the eth or wla names traditionally used. For example: enp5s0 . Warning Red Hat does not support systems with consistent device naming disabled. For further details, see Is it safe to set net.ifnames=0? 11.1. Naming Schemes Hierarchy By default, systemd will name interfaces using the following policy to apply the supported naming schemes: Scheme 1: Names incorporating Firmware or BIOS provided index numbers for on-board devices (example: eno1 ), are applied if that information from the firmware or BIOS is applicable and available, else falling back to scheme 2. Scheme 2: Names incorporating Firmware or BIOS provided PCI Express hotplug slot index numbers (example: ens1 ) are applied if that information from the firmware or BIOS is applicable and available, else falling back to scheme 3. Scheme 3: Names incorporating physical location of the connector of the hardware (example: enp2s0 ), are applied if applicable, else falling directly back to scheme 5 in all other cases. Scheme 4: Names incorporating interface's MAC address (example: enx78e7d1ea46da ), is not used by default, but is available if the user chooses. Scheme 5: The traditional unpredictable kernel naming scheme, is used if all other methods fail (example: eth0 ). This policy, the procedure outlined above, is the default. If the system has biosdevname enabled, it will be used. Note that enabling biosdevname requires passing biosdevname=1 as a kernel command-line parameter, except in the case of a Dell system, where biosdevname will be used by default as long as it is installed. If the user has added udev rules which change the name of the kernel devices, those rules will take precedence.