This article is a sort of “Post-it®”, a brief explanation of how to configure a network bridge with two NICs under CentOS 5.x / 6.x. After spending more than 10 minutes googling how to perform this task ( mainly reading about ( l ) users that didn’t have a clue about what a network bridge is or, worse, asking how to bridge n-thousand VM while performing routing having iptables misconfigured… ), I thought it was better to write everything down in “safe place”: what’s better than my blog?

So, this is how I have made the bridge on Nighthawk ( a double Pentium III – 800 MHz with a Gig of RAM and a pair of UWSCSI3 disks ), under CentOS 6.0.
The two NICs are both based on an Intel 82559 chip. The first one is integrated into the motherboard, while the second one is on a PCI slot.

OBVIOUSLY, a network bridge has ONE MAC address ( could be the same of one of the two NIC or could be a different one ) and ONE IP address, unless your playing with aliased interface over a bridge, but this is not the case.

The integrated NIC is eth0, the NIC on the PCI slot is eth1 while the network bridge is nbr0.

So, these are the configuration files:

# /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE="eth0"
HWADDR="00:30:48:AA:BB:CC"
ONBOOT="yes"
BRIDGE="nbr0"

# /etc/sysconfig/network-scripts/ifcfg-nbr0
DEVICE="nbr0"
TYPE="bridge"
BOOTPROTO="dhcp"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
ONBOOT="yes"

The bridge takes its IP address via DHCP. If a static address is required, file ifcfg-nbr0 must be changed according to what is reported into the RHEL Deployment Guide.

Bye

And I’m saying goodbye, not farewell!

By the way, I moved from Debian “Squeeze” ( 6.0 testing ) to CentOS 5.5 on Tomcat and, even with an older 2.6.18 kernel (compared to the newer 2.6.32 debian’s one) everything worked flawlessly: video, network card, audio.

I must admit that Tomcat is a little old, but the battery is still alive and it’s powerful enough for many of my daily task, like writing small programs, reading e-mails, surfing the web, doing some electronic projects, using office apps etc.

It is not that I don’t like Debian anymore. I was using a testing distribution and I had only minor issues, so I was quite happy with it.

Then Hyper-V came: a powerful virtualization service for Windows Server 2008 that is also able to run Linux as a guest OS. Great, but it only works with SLES or RHEL. You can obtain SLES for free but you will have only two month of updates without purchasing a subscripition with Novell. On the other hand, you can’t have RHEL for free, but you can have CentOS and upgrades for free, so I went for CentOS. I currently have a VM running CentOS with the Linux integrations services installed that works well.

I did a backup of all the data on Tomcat and installed CentOS on it. It works perfectly beside Windows XP on the another partition.

Recently, I have also installed CentOS on Nighthawk. I use it remotely via SSH or VNC.
I’m slowly getting accustomished to yum, even if sometimes I still type apt-get instead of yum… oh well.

However, my “goodbye” to Debian isn’t really true, because as of writing this post, this page is being served by apache running on a Debian 4.0 virtual machine according to the informations tophost gives me on the site’s control panel…

Bye