Changing the ethX to Ethernet Device Mapping in EL6 and Fedora 12 to 14

AN!Wiki :: How To :: Changing the ethX to Ethernet Device Mapping in EL6 and Fedora 12 to 14

WARNING: Currently being updated, please don't follow this How-To yet.

When you have two or more ethernet devices in one machine, the Fedora install may not install them in the order you want. This document will show you how to change the ethX to physical ethernet device mapping.

This is desirable in cases where specific network cards need to be used on specific networks, and you are interested in maintaining common ethX names across servers. A practical example is found in the Two Node Fedora 13 Cluster project.

For the Impatient

Assuming that NetworkManager is already removed.

/etc/init.d/network stop
vim /etc/sysconfig/network-scripts/ifcfg-eth*
# Make changes as needed
vim /etc/udev/rules.d/70-persistent-net.rules
# Make changes as needed
start_udev
/etc/init.d/network start

Thanks for fenris02 and mutk

Example

I find it easier to follow instructions when I have an example to follow, so let me provide one here:

Desired Mapping

Let's assume that you want this:

• eth0
  • MAC: 90:E6:BA:71:82:D8
• eth1
  • MAC: 00:21:91:19:96:5A
• eth2
  • MAC: 00:0E:0C:59:45:78

Initial Mapping

Now lets assume you got this:

• eth0
  • MAC: 00:21:91:19:96:5A
• eth1
  • MAC: 90:E6:BA:71:82:D8
• eth2
  • MAC: 00:0E:0C:59:45:78

The Problem

In the above example, eth2 is where we want it, so we leave it alone. The problem is that eth0 and eth1 are reversed.

The Fix

Traditionally, the ethX to physical ethernet device was linked via the HWADDR=... argument in each NIC's ifcfg-ethX configuration file. With the introduction of udev, the HWADDR=... is no longer needed. Instead, this mapping is now made in the 70-persistent-net.rules udev configuration file.

First, stop network. This is important because if you change the MAC address to ethX mapping while the network is still up, the initd script will fail to bring down the network devices and you will need to reboot for the changes to take effect.

/etc/init.d/network stop

We'll need to work in two directories;

• /etc/sysconfig/network-scripts/
  • Where the interface configuration files exist.
• /etc/udev/rules.d/
  • Where the udev configuration files exist.

Interface Configuration

Go to /etc/sysconfig/network-scripts/ and then use cat to see the contents of the ifcfg-eth* network configuration files:

cd /etc/sysconfig/network-scripts/
cat ifcfg-eth0
cat ifcfg-eth1
cat ifcfg-eth2

This will produce output something like this:

cd /etc/sysconfig/network-scripts
cat ifcfg-eth*

# D-Link System Inc DGE-560T PCI Express Gigabit Ethernet Adapter
HWADDR=00:21:91:19:96:5A
DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
TYPE=Ethernet
IPADDR=192.168.1.71
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
DNS1=192.139.81.117
DNS2=192.139.81.1
DEFROUTE=yes

# Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller
HWADDR=90:E6:BA:71:82:D8
DEVICE=eth1
BOOTPROTO=static
ONBOOT=yes
TYPE=Ethernet
IPADDR=10.0.0.71
NETMASK=255.255.255.0

# Intel Corporation 82540EM Gigabit Ethernet Controller
HWADDR=00:0E:0C:59:45:78
DEVICE=eth2
BOOTPROTO=static
ONBOOT=yes
TYPE=Ethernet
IPADDR=10.0.1.71
NETMASK=255.255.255.0

The important lines are the DEVICE=... and HWADDR=... lines. The rest of the lines will very likely differ from the output above, and most will likely be set to BOOTPROTO=static. One or more may also be set to ONBOOT=yes. It is outside the scope of this tutorial to cover the various settings

With networking stopped, all we need to do is change the HWADDR=... lines in ifcfg-eth0 to have the MAC address from ifcfg-eth2 and vice-versa. For an exhaustive list of available options, please see the Fedora documentation.

To rearrange the mappings, simply change around the HWADDR=... values in the ifcfg-eth* files so that the desired MAC address and DEVICE=... are in the same file. Personally, I like to move around the comment at the top that names the NICs, also. Here is the updated files:

cat ifcfg-eth*

# Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller
HWADDR=90:E6:BA:71:82:D8
DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
TYPE=Ethernet
IPADDR=192.168.1.71
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
DNS1=192.139.81.117
DNS2=192.139.81.1
DEFROUTE=yes

# D-Link System Inc DGE-560T PCI Express Gigabit Ethernet Adapter
HWADDR=00:21:91:19:96:5A
DEVICE=eth1
BOOTPROTO=static
ONBOOT=yes
TYPE=Ethernet
IPADDR=10.0.0.71
NETMASK=255.255.255.0

# Intel Corporation 82540EM Gigabit Ethernet Controller
HWADDR=00:0E:0C:59:45:78
DEVICE=eth2
BOOTPROTO=static
ONBOOT=yes
TYPE=Ethernet
IPADDR=10.0.1.71
NETMASK=255.255.255.0

'udev' Configuration

The user-space device manager, udev, maintains a list of configuration files that help ensure that hardware to /dev (software) mappings stay consistent, even when hardware is hot swapped or moved between physical connections. For networking hardware, this mapping is recorded in the 70-persistent-net.rules.

Here, all that needs to be done is for the NAME="..." entry to be changed to reflect what you want. Note that the entries do not need to be in any particular order.

cd /etc/udev/rules.d/
cat 70-persistent-net.rules

# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# PCI device 0x10ec:0x8168 (r8169) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="90:e6:ba:71:82:d8", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

# PCI device 0x1186:0x4b00 (sky2) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:21:91:19:96:5a", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

# PCI device 0x8086:0x100e (e1000) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0e:0c:59:45:78", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth2"

Make the changes and save the file. Continuing with this example, the file should now look like this:

cd /etc/udev/rules.d/
cat

# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# PCI device 0x10ec:0x8168 (r8169) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="90:e6:ba:71:82:d8", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

# PCI device 0x1186:0x4b00 (sky2) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:21:91:19:96:5a", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

# PCI device 0x8086:0x100e (e1000) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:0e:0c:59:45:78", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth2"

Making the Changes Take Effect

First, you need to reload udev so that it updates the mapping in memory. This is done using the start_udev program:

start_udev

Starting udev:                                             [  OK  ]

With udev updated, the last step is to restart the network daemon:

/etc/init.d/network start

Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:                                [  OK  ]
Bringing up interface eth1:                                [  OK  ]
Bringing up interface eth2:                                [  OK  ]

Done! use ifconfig to verify that the network cards are properly assigned to the specified ethX names.

Caveat!

NOTE: If you are using a vlan, the device facing the vlan can not have the HWADDR=... value set! Set the others and leave this commented out. Otherwise, because of how the vlan loads, the OS will not see the physical device and will fail to bring up the interface at all.

 

Any questions, feedback, advice, complaints or meanderings are welcome.
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