How To Change MTU on Virtual Iron V4 Nodes

This is a quick first draft & works for a simple network_config_directives.xml with only one static interface IP & no routes in it. However it may work if you have more than one interface with a static IP as long as you add an MTU directive for each interface even though you only set it to 1500. It will only work for static assignments, DHCP is not supported.

However, on the up side it is fairly easy to do and very simple to put back if it doesn't work for you; just restore the original (re-named) initramfs.cpio.gz, configure_node and delete the line(s) you added to your network_config_directives.xml files.

Changing the MTU on Virtual iron 4 Nodes.

The managed nodes in Virtual Iron are configured by scripts downloaded via http from the Virtualisation Manager Server.

The configuration scripts are part of the initial ram disk file system that is downloaded by TFTP when a node boots, it then pulls configuration data and a further script to configure the node.

The main steps needed to acheive the modification are to extract the filesystem, initramfs.cpio.gz, and replace a couple of scripts and re-assemble the archive.

Final steps are to modify the xml network config, and copy over the modified node configuration file.

You need to do this as root (which can be dangerous to your filesystem), or do it as an ordinary user then su to root chown all the files before re-assembling the filesysetm image.

Make somewhere to work

mkdir $HOME/tmp
cd $HOME/tmp

Copy and uncompress the initramfs

cp /opt/VirtualIron/VirtualizationManager/bootfiles/microkernel/RELEASE/initramfs.cpio.gz .
gzip -d initramfs.cpio.gz

Extract the initramfs, be very careful not to over write your file system when extracting the CPIO archive,
note the --no-absolute-filenames switch!! Read warning above.

cpio -i -d -H newc -F initramfs.cpio --no-absolute-filenames

Delete no longer required fs and move back a directory.

rm -f initramfs.cpio.gz
cd ..

Get the modded files, uncompress and copy to final destinations

wget http://theinternet.org.uk/downloads/mtufiles.tar.gz
tar -zxvf mtufiles.tar.gz
mv functions tmp/etc/init.d/network_scripts/
cp configure_node tmp/etc/init.d/http_node_config/

Use the mkramfs script to re-assemble the initramfs. be sure to chown all the files and syslinks as root if you extracted as an ordinary user (chown and chown -h).

./mkramfs $HOME/tmp/ initramfs.cpio.gz

Backup the original initramfs

mv /opt/VirtualIron/VirtualizationManager/bootfiles/microkernel/RELEASE/initramfs.cpio.gz \
/opt/VirtualIron/VirtualizationManager/bootfiles/microkernel/RELEASE/initramfs.cpio.gz.sav

Copy the new image to the boot directory

mv initramfs.cpio.gz /opt/VirtualIron/VirtualizationManager/bootfiles/microkernel/RELEASE/

Now edit your network directives file for each node and add an mtu line eg. 9000 ,the mtu will default to 1500 if you don't.

/opt/VirtualIron/VirtualizationManager/bootfiles/boot/00-E0-00-00-1A-AB/network_config_directives.xml

<?xml version="1.0" encoding="UTF-8"?>
<NETWORKCFGDIRECTIVES>
    <CFGNICSTATIC>
        <INTERFACE>00-E0-00-00-1A-AB</INTERFACE>
        <STATICIP>192.168.0.1</STATICIP>
        <STATICIPMASK>255.255.255.0</STATICIPMASK>
        <STATICIPMTU>9000</STATICIPMTU>
    </CFGNICSTATIC>
</NETWORKCFGDIRECTIVES>

Finally copy the configure_node file over the one in each node directory (backup first) where you have just edited the network_config_directives.xml file.

cp %HOME/tmp/configure_node /opt/VirtualIron/VirtualizationManager/bootfiles/boot/00-E0-00-00-1A-AB/

You can now reboot a Managed Node and check the mtu for the port in the hardware screen on your Virtualisation Manager.