Posts Tagged ‘networking’

Disable IPv6 on RHEL5 or Centos5

Monday, May 16th, 2011

Recently, bonding module requires IPv6 module. There are two possible solutions. The first is to define zeroconf to off, by adding the following line to /etc/sysconfig/network :

The other method, which actually disables IPv6 is to insert into /etc/modprobe.conf the following line:
options ipv6 disable=1

That should do the trick. You will need to restart/reload your modules, of course.

Xen Networking – Bonding with VLAN Tagging

Thursday, October 23rd, 2008

The simple scripts in /etc/xen/scripts which manage networking are fine for most usages, however, when your server is using bonding together with VLAN tagging (802.11q) you should consider an alternative.

A PDF document written by Mark Nielsen, GPS Senior Consultant, Red Hat, Inc (I lost the original link, sorry) named “BOND/VLAN/Xen Network Configuration” as a service to the community, game me few insights on the subject. Following one of its references, I saw a bit more elegant method of doing a bridging setup under RedHat, which takes managing the bridges away from xend, and leaves it at the system level. Lets see how it’s done on RedHat style Linux distribution.

Manage your normal networking configurations

If you’re using VLAN tagging over bonding, than you should have to setup a bonding device (be it bond0) which has definitions such as this:

/etc/sysconfig/network-scripts/ifcfg-eth0 and /etc/sysconfig/network-scripts/ifcfg-eth1



BONDING_OPTS=”mode=1 miimon=100″

This is rather stright-forward, and should be rather a default for such a setup. Now comes the more interesting part. Originally, the next configuration part would be bond0.2 and bond0.3 (in my example). The original configuration would have looked like this (this is in bold because I tend to fast-read myself, and tend to miss things too often). This is not how it should look when we’re done!

/etc/sysconfig/network-scripts/ifcfg-bond0.2 (same applies to ifcfg-bond0.3)


Configure bridging

To setup a bridge device for bond0.2, replace the mentioned above ifcfg-bond0.2 with this new /etc/sysconfig/network-scripts/ifcfg-bond0.2


Now, create a new file /etc/sysconfig/network-scripts/ifcfg-xenbr0


Now, on network restart, the bridge will be brought up, holding the right IP address – all done by initscripts, with no Xen intervention. You will want to repeat the last the “Configure bridge” part for any additional bridge you want to be enabled for Xen machines.

Don’t let Xen bring any bridges up

This is the last part of our drill, and it is very important. If you don’t do it, you’ll get a nice networking mess. As said before, Xen (community), by default, can’t handle bondings or vlan tags, so it will attempt to create or modify bridges to eth0 or the likes. Edit /etc/xen/xend-config.sxp and remark any line containing a directive containing starting with “network-script“. Such a directive would be, for example

(network-script network-bridge)

Restart xend and restart networking. You should now be able to configure VMs to use xenbr0 and xenbr1, etc (according to your own personal settings).

RHEL4 tends to change network interfaces names

Friday, July 6th, 2007

RHEL4 tends to change the names of network cards when there are more than one. If you had a NIC called eth0 during install time, it doesn’t mean that it will maintain that name after the first reboot. It could switch names with its friend, and be called now eth1, while the previous eth1 name is now eth0.

A solution using udev was posted in HPs forums, and can be reached directly through here. I will quote it:

Device persistence can also be enabled to ensure that the NICs identifying themselves as eth1, eth2, etc… always remain on the same hardware ports in case of a failure of a single NIC port. You don’t want your eth names to shift.

Upgrading to udev-095 from udev-039 that ships with RHEL4 is the smoothest solution, but that wasn’t an option for me. Using names other than eth0 – eth3 also wasn’t an option for me. Here is what we ended up using to get around udev-039’s inability to re-use eth0-ethx names.

Create a udev rule using YOUR MACS
Create an /etc/mactab file using YOUR MACS
Modify /etc/init.d/network to run nameif

KERNEL=”eth*”, SYSFS{address}=”00:0b:cd:69:c3:66″, NAME=”NIC1″
KERNEL=”eth*”, SYSFS{address}=”00:0b:cd:69:c3:65″, NAME=”NIC2″
KERNEL=”eth*”, SYSFS{address}=”00:11:0a:17:66:26″, NAME=”NIC3″
KERNEL=”eth*”, SYSFS{address}=”00:11:0a:17:66:27″, NAME=”NIC4″

eth0 00:0b:cd:69:c3:66
eth1 00:0b:cd:69:c3:65
eth2 00:11:0a:17:66:26
eth3 00:11:0a:17:66:27

(add right after
# Check that networking is up.
[ “${NETWORKING}” = “no” ] && exit 0

# RDD: add ‘nameif’ usage; uses /etc/mactab
nameif || echo “nameif: reports error”