Appendix A. Consistent Network Device Naming

Red Hat Enterprise Linux 6 provides consistent network device naming for network interfaces. This feature changes 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…], 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.
The new naming convention assigns names to network interfaces based on their physical location, whether embedded or in PCI slots. By converting to this naming convention, system administrators will no longer have to guess at the physical location of a network port, or modify each system to rename them into some consistent order.
This feature, implemented via the biosdevname program, will change the name of all embedded network interfaces, PCI card network interfaces, and virtual function network interfaces from the existing eth[0123…] to the new naming convention as shown in Table A.1, “The new naming convention”.

Table A.1. The new naming convention

Device Old Name New Name
Embedded network interface (LOM) eth[0123…] em[1234…][a]
PCI card network interface eth[0123…] p<slot>p<ethernet port>[b]
Virtual function eth[0123…] p<slot>p<ethernet port>_<virtual interface>[c]
[a] New enumeration starts at 1.
[b] For example: p3p4
[c] For example: p3p4_1
System administrators may continue to write rules in /etc/udev/rules.d/70-persistent-net.rules to change the device names to anything desired; those will take precedence over this physical location naming convention.

A.1. Affected Systems

Consistent network device naming is enabled by default for a set of Dell PowerEdge, C Series, and Precision Workstation systems. For more details regarding the impact on Dell systems, visit
For all other systems, it will be disabled by default; refer to Section A.2, “System Requirements” and Section A.3, “Enabling and Disabling the Feature” for more details.
Regardless of the type of system, Red Hat Enterprise Linux 6 guests running under Red Hat Enterprise Linux 5 hosts will not have devices renamed, since the virtual machine BIOS does not provide SMBIOS information. Upgrades from Red Hat Enterprise Linux 6.0 to Red Hat Enterprise Linux 6.1 are unaffected, and the old eth[0123…] naming convention will continue to be used.