Oracle Labs by Yuri Khazin, Oracle DBA

April 14, 2016

RHEL 6.7, OEL 6.7 network adapters configuration and VM cloning


Cloning of a virtual machine in Oracle’s VB (Virtual Box) presents a particular pain. The exact clone, of course, is created with same MAC and IP addresses for all NICs present. Great for some purposes, not so great if you wanted a duplicate to repurpose. Then you would have reinitialized MACs during or after cloning and your trouble would start as all NICs in the clone won’t be functional upon power up. In older Linux distribution all you had to do is edit MAC addresses in the ifcfg-eth* files in /etc/sysconfig/network-scripts and that was it. Not so now.

In Linux 6 (Red Hat, Fedora, Centos) the hardware device control is primarily done by udev system and by NetworkManager service. This is an out of the box configuration. In the following exercise we will look at a case of a virtualized OEL 6.7 Server, which is a non-GUI Oracle’s package based on RHEL 6.7

Why Server edition? Because it is a headless, non-GUI distro, where all management needs to be done via command line and not through the nice desktop tools.

As stated above, in Linux 6 the udev system looks after changes in hardware and enumerates new NICs while preserving the old NIC records. Both parts are now present in this file: /etc/udev/rules.d/70-persistent-net.rules

Therefore, your /etc/sysconfig/network-scripts/ifcfg-eth* files are now not in sync with persistent rules. We will look at how they should be reconciled.

A few additional notes:

  • In my practice with OEL 6.7 the system-config-network-tui tool had no effect on configuration so I don’t recommend using it
  • Don’t just edit /etc/sysconfig/network-scripts/ifcfg-eth* files after cloning, read this article to the end to understand why you need to examine and change the udev part
  • OEL 6.7 Server (and probably Red Hat, Centos and Fedora distros) come with sshd server preconfigured with some annoying security features that make ssh login very slow. If you went through this article and still have issues logging into your machine you may need to read this guide about “Fixing SSH login long delay”

So, let’s start:

On original machine our network configuration is as follows:

eth0 is an adapter with static IP connected to host-only network

eth1 is an adapter with DHCP connected to NAT network

Both are running

Following are their respective config files

[root@oms1 network-scripts]# cat ifcfg-eth0
DEVICE=eth0BOOTPROTO=none

ONBOOT=yes

IPADDR=20.20.10.21

NETMASK=255.255.255.0

[root@oms1 network-scripts]# cat ifcfg-eth1
DEVICE=eth1HWADDR=08:00:27:F9:3C:34

TYPE=Ethernet

ONBOOT=yes

NM_CONTROLLED=yes

BOOTPROTO=dhcp

Notice, that although ifcfg-eth1 contains HWADDR keyword it is not required and can be removed when udev is allowed to manage the hardware.

Below is the contents of persistent rules (before cloning). Sometimes after cloning, the order of devices may be mixed up, so pay close attention to MAC addresses and then assign the desired names in proper order.

/etc/udev/rules.d/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 0x8086:0x100f (e1000)

SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”08:00:27:7d:f0:88″, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth0″

# PCI device 0x8086:0x100e (e1000)

SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”08:00:27:f9:3c:34″, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth1″

After cloning with MAC address re-initialized the machine comes up like this (new NICs detected but since there are no matching ifcfg-eth* files the NICs are inactive):

Old NICs are eth0 and eth1, the new ones are eth2 and eth3

Delete old NICs:

Rename the ordering of NICs:

Make sure ifcfg* files match (optionally change the static IP)

Make sure original machine is NOT online as the clone will try to come up with same static IP. Reboot the clone machine (necessary, because of change to persistent rules)

After reboot of the clone:

If you want to change the static IP you can do it in ifcfg-eth0 and then restart networks

service network restart

Acknowledgements and references:

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