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Martin Willi, 14.05.2008 15:45


= Dynamic Uml Mesh Modeler =
''Dumm'' is a framework to set up a virtual network using user mode linux guests.
It cleverly glues together some nice technologies to build networks dynamically.
To change the network topology, hosts are not required to reboot, changes apply
instantly and configuration can be done on the host (no network connection
required to change anything).

Status
''Dumm'' is currently highly experimental and [source:trunk/src/dumm incomplete]. A prototype is running
and a proof of concept has shown that it works.
Along with the ''dumm'' library, a graphical GTK client is in developement to interactively set
up and reconfigure UML networks. The UML network of the old UML framework can be simulated with another tool.

The graphical client is incomplete. It is missing: * Removal of added switches * Disconnecting guests from switches * Scenario management

The framework itself is also missing some features: * Configuring addresses/routes in guests through hosts * Invoke commands on guests without ssh * Scenario scripting

Why UML?
UML is a senior in vitualization technologies, and there is a lot of new
hyped stuff about virtualization around. However, UML is lightweight, easy to
set up and allows dynamic reconfiguration (e.g. add/remove interfaces at
runtime), allows access to the hosts filesystem through hostfs and has some
other neat features.
Performance is not critical for our needs, and maybe we get hardware
virtualization support soon in UML.
It is free and fits perfectly. Requirements * Host: * Kernel: * A recent 2.6 kernel * [http://www.user-mode-linux.org/~blaisorblade/patches/skas3-2.6/ SKAS3 patch] recommended * [http://fuse.sourceforge.net/ FUSE] enabled * support for TAP devices * Userland: * [source:trunk/src/libstrongswan libstrongswan] * libbridge from [http://linux-net.osdl.org/index.php/Bridge bridge-utils] * GTK+2 with developement headers * Gnome !VteTerminal with developement headers * Guest: * Kernel: * hostfs * tuntap networking * mcast networking * Userland: * none Architecture

=== Working set ===
Dumm needs a directory to store all its files, guest configurations and other
stuff. Inside that working directory, you'll find:

{{{
workingdir/ - root folder containing a set of hosts and scenarios
guests/ - contains all created guests
alice/ - subdirectory for host "alice"
alice/ - UML created folder (named umid) containing UML runtime files
mem - memory configuration file (contains amount of guest memory in MB)
linux - symlinked UML kernel this host uses
master/ - symlinked master root file system for this host
diff/ - copy-on-write overlay to master this host uses
union/ - mounted unified filesystem (master + diff + optional scenario)
bob/
... - same stuff as in alice
scenarios/ - contains all scenarios
test1/ - a scenario folder
diff/ - copy-on-write overlays for each guest's union folder
alice/ - COW for alice
bob/ - COW for bob
config - network configuration file
}}}

=== Networking ===
Network connectivity is realized through tap devices. When creating a ''eth0''
network device on ''alice'', a ''alice-eth0'' tap device appears on the host. These
are directly connected, when ''alice'' sends traffic to ''eth0'', it appears on the
host at ''alice-eth0''. You can see that as a small network segment (or just a
cable), where these interfaces are attached directly.
To build larger network segments, linux bridging on the host comes into play.
Segments are created by creating a bridge (as with brctl), and then attaching
our tap devices to that bridge. Routing can be done on a UML guest, or even on
the host.
This setup has some advantages over the ''uml_switch'' solution. Bridging works
more reliable in the kernel, and as we see every network interface on the host,
we can sniff at every interface to get some clue what the guests are doing.

Howto
In this mini-howto, we build and boot a minimalistic debian guest on a ubuntu host.
We do everything as root here to simplify things!

=== Host setup === * install required packages: {{{
aptitude install libfuse-dev libgtk2.0-dev libvte-dev
}}} * install libbridge: {{{
git clone git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/bridge-utils.git
cd bridge-utils
autoconf
./configure
cd libbridge
make
make install
}}} * Build and install strongSwan from SVN sources. {{{
svn co www.strongswan.org/ikev2/trunk strongswan
cd strongswan
less HACKING
./autogen
./configure --enable-dumm [other options]
make
make install
}}}

=== Guest master filesystem setup === * create a clean directory and a directory for our master filesystem in it: {{{
mkdir umldir
cd umldir
mkdir master
}}} * bootstrap a debian sid system into master: {{{
debootstrap sid master http://mirror.switch.ch/ftp/pub/debian/
}}} * enter chroot {{{
chroot master
}}} * enable login on tty0 {{{
echo "0:2345:respawn:/sbin/getty 38400 tty0" >> /etc/inittab
echo "tty0" >> /etc/securetty
}}} * Enable main repository {{{
echo deb http://mirror.switch.ch/ftp/pub/debian sid main contrib > /etc/apt/sources.list
aptitude update
}}} * Install proper locales support {{{
aptitude install locales
dpkg-reconfigure locales
}}} * Install some packages for strongSwan {{{
aptitude install libgmp3c2 libsqlite3-0 libcurl3 dropbear gdb binutils
}}} * leave chroot {{{
exit
}}} * build a vanilla UML kernel (using [http://trac.strongswan.org/attachment/wiki/DynamicUmlMeshModeler/.config my config]): {{{
wget http://kernel.org/pub/linux/kernel/v2.6/linux-2.6.22.1.tar.bz2
tar jxvf linux-2.6.22.1.tar.bz2
cd linux-2.6.22.1
make mrproper
wget http://trac.strongswan.org/attachment/wiki/DynamicUmlMeshModeler/.config?format=raw -O .config
ARCH=um make menuconfig
ARCH=um make
}}}

=== Start a network ===
You'll have to run the tools as root. Make sure you have a DISPLAY set, e.g. by starting it under ''sudo''. * Invoke the graphical client {{{
sudo ipsec dumm
}}}
Add guests, select our master filesystem and the compiled kernel. Add a bridges and connect your guests to it.
Start your guests and configure them. {{{
sudo ipsec testing
}}}

  • The default strongSwan UML scenario is created by running
Installing strongSwan on guests
As we have full access to the master filesystem on the host, we can build strongSwan on the host and install it to the guests {{{
cd path/to/strongswan/
DESTDIR=/full/path/to/master make install
}}}