Interface names

6.10 LPAR mode z/VM guest KVM guest

Most interface names are assigned by device drivers.

Names assigned by device drivers

Most interface names that Linux assigns are of the form <prefix><n> where <prefix> depends on the interface type. <n> is an index number that identifies an individual interface of a particular type.

Table 1 summarizes the prefixes that network device drivers use for interfaces that are associated with real hardware.

Table 1. Interface prefixes for real devices
Prefix	Interface type	Device driver module	Hardware
eth	Ethernet	qeth, lcs, mlx5_core	OSA-Express, RoCE Express features
ctc	Channel-to-Channel	ctcm	ESCON channel card, FICON® channel card
mpc	Channel-to-Channel	ctcm	ESCON channel card
hsi	HiperSockets	qeth	Real HiperSockets

Table 2 summarizes the prefixes that network device drivers use for interfaces that are associated with virtual hardware:

Table 2. Interface prefixes for virtual devices
Prefix	Interface type	Device driver module	Comment
hsi	HiperSockets, virtual NIC	qeth	Virtual NIC-type HiperSockets coupled to a guest LAN
eth	virtual NIC	qeth	QDIO virtual NIC coupled to a guest LAN or virtual switch
eth	virtual NIC	virtio_net	virtio virtual NIC
ctc	virtual Channel-to-Channel	ctcm	virtual CTCA
mpc	virtual Channel-to-Channel	ctcm	virtual CTCA
iucv	IUCV	netiucv	IUCV authorizations are required

When the first interface name for a particular type is created, it is assigned the index number 0, the second is assigned 1, the third 2, and so on. For example, the first HiperSockets interface is named hsi0, the second hsi1, the third hsi2, and so on.

When a network device is set offline, it retains its interface name. When a device is removed, it surrenders its interface name and the name can be reassigned as network devices that are defined in the future. When an interface is defined, the Linux® kernel always assigns the interface name with the lowest free index number for the particular type. For example, if the network device with an associated interface name hsi1 is removed while the devices for hsi0 and hsi2 are retained, the next HiperSockets interface to be defined becomes hsi1.

Persistent names assigned by other means

In Linux distributions, a user-space component typically assigns a persistent name to the network interface, for example enc+device number for OSA and HiperSockets. or eno+UID or ens + FID for ROCE, see RoCE Express.

Often these components rename the interfaces quickly, and you might see multiple instances of [interface_name]: renamed from eth0 in the log file.

These interface names are retained when a device is set offline. The user-space components typically ensure that the names are persistent even if a device is removed and hot-plugged or if the Linux instance is rebooted.

Table 3. Persistent interface names
Prefix	Interface type	Comment
enc	HiperSockets, OSA	Real HiperSockets or virtual NIC type HiperSockets coupled to a guest LAN
eno \| ens	Ethernet	PCI-based network devices

Your distribution might provide a way to track the mapping or to assign meaningful names to your interfaces.