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RHEL 7 / CENTOS 7 USE CLASSIC ETH0 STYLE DEVICE

WHY WAS IT CHANGED ?

Red Hat Enterprise Linux 7 introduced a new scheme for naming network devices called “Consistent Device Naming”. It’s called Consistent Device Naming because previously the name of the devices [eth0,eth1,eth2] was completely dependant upon the order the kernel detected them as it booted. In certain circumstances, such as adding new devices to an existing system, the naming scheme could become unreliable.

FURTHER READING

The official Red Hat 7 Documentation on consistent device naming can be found here.

WHAT DOES THE NEW SCHEME LOOK LIKE ?

# ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eno16777736: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
 link/ether 00:0c:29:89:1b:2e brd ff:ff:ff:ff:ff:ff

HOW DO I CHANGE IT BACK TO ETH[0-9] STYLE NAMING ?

In summary we need to

  • Add extra parameters to the kernel configuration
  • Add this to the boot configuration
  • Restart the machine
  • Move the existing interfaces to the new scheme
  • Restart the network service

ADD EXTRA PARAMETERS TO THE KERNEL CONFIGURATION

Modify the grub bootloader to pass some extra parameters to the kernel at boot time. The kernel will then use these options to decide which naming scheme to use.

First we backup and edit the grub configuration file.

# cp /etc/default/grub /etc/default/grub.bak

Then we can safely edit the grub configuration file

# vim /etc/default/grub

The config file will look similar to the following

GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet "
GRUB_DISABLE_RECOVERY="true"

The line that starts “GRUB_CMDLINE_LINUX” needs to have some extra paramters added.

The extra parameters are

biosdevname=0 net.ifnames=0

So the final file looks like

GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet biosdevname=0 net.ifnames=0 "
GRUB_DISABLE_RECOVERY="true"

ADD THIS TO THE BOOT CONFIGURATION

If you are using a UEFI system then rebuild grub with this command

grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

Otherwise use the following

# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-327.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-327.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-3c913eca0eab4ebcb6da402e03553776
Found initrd image: /boot/initramfs-0-rescue-3c913eca0eab4ebcb6da402e03553776.img
done

RESTART THE MACHINE

Now we will restart the host, and the new naming scheme will take effect on reboot.

# shutdown -r now

MOVE THE EXISTING INTERFACES TO THE NEW SCHEME

It’s possible you may now need to reconfigure your network interface.

Here you can see the network interface is up, however there is no IP information associated with the new device name.

# ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
 link/ether 00:0c:29:89:1b:2e brd ff:ff:ff:ff:ff:ff

For this example we will assume i’m not using NetworkManager. Therefore I’ll be editing the network configuration files in /etc/sysconfig/network-scripts directly.

Change into the network scripts directory.

# cd /etc/sysconfig/network-scripts/

Rename the old interface configuration file to new scheme

# mv ifcfg-eno16777736 ifcfg-eth0

Update the contents of the configuration file to use the new scheme

# sed -i 's/eno16777736/eth0/' ifcfg-eth0

mv ifcfg-eno16777736 ifcfg-eth0
vi /etc/udev/rules.d/90-eno-fix.rules
# This file was automatically generated on systemd update
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:29:9e:8f:95", NAME="eno16777736"

# This file was automatically generated on systemd update
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0c:29:9e:8f:95", NAME="eth0"


RESTART THE NETWORK SERVICE

Finally restart the network service so the changes take effect.

# systemctl restart network

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