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Eric Leschinski
Asked: 2012-10-24 06:17:01 +0800 CST

Fedora 17 ifconfig eth0 returns an error message, why did linux change eth0 to em1?

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I have a fresh install of Fedora 17 installed, 64 bit. Everything works flawlessly, It connects to the internet automatically when I plug in the internet cable.

So I'm kind of confused when I issue this command:

el@defiant ~ $ ifconfig eth0

And I get the error:

eth0: error fetching interface information: Device not found

Device not found? Here is ifconfig:

ifconfig

I get this:

em1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
    inet 192.168.1.102  netmask 255.255.255.0  broadcast 192.168.1.255
    inet6 fe80::ea40:f2ff:fee1:58c  prefixlen 64  scopeid 0x20<link>
    ether e8:40:f2:e1:05:8c  txqueuelen 1000  (Ethernet)
    RX packets 44753  bytes 51284267 (48.9 MiB)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 34222  bytes 4294174 (4.0 MiB)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
    device interrupt 20  memory 0xf7d00000-f7d20000  

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 16436
    inet 127.0.0.1  netmask 255.0.0.0
    inet6 ::1  prefixlen 128  scopeid 0x10<host>
    loop  txqueuelen 0  (Local Loopback)
    RX packets 5152  bytes 1263744 (1.2 MiB)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 5152  bytes 1263744 (1.2 MiB)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

So, it appears that someone has changed the old eth0 to em1 since earlier versions of Fedora (Fedora 8 is the last I know which used eth0). If I do the command: ifconfig em1 then I get something similar to the old ifconfig eth0. But why the name change?

My question is why was eth0 changed to em1 and what the heck does em from em1 mean?

linux

2 Answers

  1. Best Answer

    It's consistent network device naming.

    Systems, particularly servers, with multiple network ports, name the ports ethX in a non-deterministic order, and are therefore not useful for system administrators.

    System Administrators can then use BIOS-provided names, which are consistent and not arbitrarily named, for their network ports. This eliminates the confusion that non-deterministic naming brings, and eliminates the use of hard-coded MAC address based port renaming which a) is racy and error-prone, and b) introduces state into an otherwise stateless system.

    This change affects most desktop, notebook, and server-class systems.

    The em means that the interface is embedded onto the motherboard. Other names apply for add-on cards: p#p# names refer to PCI (and its modern derivatives) expansion cards, where the first number is the slot on the motherboard which they're plugged into, the second number is the port on the card (a card may contain multiple ports) and the third number, if present, is a virtual function number.

    If it really bothers you, you can rename the interface to anything you want.

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  2. Fedora 15 has broke the conventional ethX naming scheme used for Ethernet devices by adopting a new scheme called Consistent Network Device Naming.

    The old ethX naming scheme works fine as long as the system has only one Ethernet port.

    However if there are more than one Ethernet ports, a sort of race condition develops at every system boot and the ports may get their names in an arbitrary order. The names will be allocated arbitrarily. This is generally not a problem in personal computers because there is only one port. However, some servers have multiple Ethernet ports and this naming scheme creates problems in such cases.

    The new naming scheme is as follows:

    em[1-N] for on-board (embedded) NICs (# matches chassis labels)

pci<slot>#<port> for cards in PCI slots, port 1..N

NPAR & SR-IOV devices add a suffix of _<vf>, from 0..N depending on the 
    number of Partitions or Virtual Functions exposed on each port.

Other Linux conventions, such as .<vlan> and :<alias> suffixes remain 
    unchanged and are still applicable.

    The new naming scheme is more complicated than the ethX scheme no doubt. But it will not make any difference to most personal computers as they generally have only a single Ethernet port. This change will not affect the Wireless and USB devices.

    illuminating links:

    Ethernet device naming change, tempest in a teacup:

    http://digitizor.com/2011/01/25/fedora-15-network-device-naming/

    http://docs.fedoraproject.org/en-US/Fedora/16/html/System_Administrators_Guide/appe-Consistent_Network_Device_Naming.html

    http://arachnoid.com/linux/network_names/index.html

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