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Network Card Settings in CentOS/RHEL


How to create Virtual (alias) Interface for Ethernet in Linux

 Why do we need multiple Alias Interfaces?

Ex :  Let me consider hosting multiple Website/FTP sites on a Single server and each website to be accessed using a different IP address. In this case, let me consider we need to host 10 websites each one to be access with a different IP address,  then we need 10 NIC cards with one IP address each on the Card which results in increased cost, space and maintenance. This can be overcome with a single Physical Network card with multiple Virtual Interfaces. Here all virtual NIC will share the MAC address of eth0 physical interface.

Case 1 :

To create a range of alias interfaces

Create the following /etc/sysconfig/network-scripts/ifcfg-eth0-range0:

IPADDR_START=<start ip address>
IPADDR_END=M<end IP address>
CLONENUM_START=0
NETMASK=<network mask>

Example :

IPADDR_START=192.168.10.20
IPADDR_END=192.168.10.30
CLONENUM_START=0
NETMASK=255.255.255.0

 Here alias interfaces will be created starting from eth0:0 to eth0:10, eth0:0 will be having 192.168.10.20 to eth0:10 will be having ip address 192.168.10.30

/etc/rc.d/init.d/network restart

Case 2:

Let me consider a requirement with only one alias network card.

Here we can follow the below steps

# cp /etc/sysconfig/network-scripts/ifcfg-eth0  /etc/sysconfig/network-scripts/ifcfg-eth0:0

# vi /etc/sysconfig/network-scripts/ifcfg-eth0:0

Replace line DEVICE=eth0 to DEVICE=eth0:0 and change the IPADDRESS as per the requirement and

# /etc/init.d/network restart

If you want the virtual IP address come up on boot, you need to replace

 ONBOOT=YES 

 to

 ONPARENT=YES

 This makes the interface only come up when the parent interface comes up, while ONBOOT=YES would pull up the parent interface even if that is configured to not come up on boot.

To make the changes take effect please restart the network services using:

# /etc/init.d/network restart

 

Setup Speed/Duplex settings on a network card in CentOS/Redhat 5.x

 Verify the required packages are installed

# rpm –qa ethtool net-tools
If not already installed, follow the below command

#yum install ethtool net-tools

Add line to the configuration file of the network card, like /etc/sysconfig/network-scripts/ifcfg-eth0

ETHTOOL_OPTS=”autoneg off speed 1000 duplex full”

Execute the below commands to make the changes take effect.

Note : Before doing this change, verify if your switch supports this configuration. Else your network cards will not function anymore.

#ifdown eth0

#ifup eth0

To verify the changes

# ethtool eth0   

For temporary change with ethtool, execute the below command:

# ethtool -s eth0 speed 1000 duplex full

For temporary change with mii-tool, execute the below command:

Disable auto-negotiation, and force the MII to 1000baseTx-FD

# mii-tool -F 1000baseTx-FD

One response to “Network Card Settings in CentOS/RHEL

  1. Chester March 17, 2013 at 8:00 am

    Hello, everything is going nicely here and ofcourse every one
    is sharing facts, that’s actually good, keep up writing.

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