Dynamic Uml Mesh Modeler » History » Version 9

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Martin Willi, 01.04.2008 09:09

= 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).

''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 console client is developed to interactively set
up and reconfigure UML networks. A test framework for strongSwan is planned around
it, and a neat GTK GUI to click together your UML network would be just lovely (someone?). Terminology * Host * The machine you are working on, has virtual guests in it. Mostly
runs on bare hardware (unless you do really fancy stuff). * Guest * Virtual UML machine running on the host. 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 * [ SKAS3 patch] highly recommended * [ FUSE] enabled * support for TAP devices * Userland: * [source:trunk/src/libstrongswan libstrongswan] * [ libreadline] * libbridge from [ bridge-utils] * Guest: * Kernel: * hostfs * consoles? * Userland: * ip (from iproute2)/netlink proxy? 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
boot.log - hosts boot console log (con0)
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)
... - 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.

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 FUSE: {{{
apt-get install libfuse-dev
}}} * install libbridge: {{{
git clone git://
cd bridge-utils
cd libbridge
make install
}}} * Build and install strongSwan from SVN sources. {{{
svn co strongswan
cd strongswan
./configure --enable-uml [other options]
make install
}}} * Ubuntu kernels almost fit our needs, they have FUSE and TAP device support. However,
SKAS3 mode is missing. Build your own kernel based on the
[ Ubuntu Howto], patched with the
[ SKAS3 patch].

=== Guest setup === * create a clean directory and a directory for our master filesystem in it: {{{
mkdir umldir
cd umldir
mkdir master
}}} * debootstrap a debian etch system into master: {{{
debootstrap etch master
echo "proc /proc proc none 0 0" > master/etc/fstab
}}} * build a vanilla UML kernel (using [ my config]): {{{
tar jxvf linux-
cd linux-
make mrproper
wget -O .config
ARCH=um make menuconfig
ARCH=um make

=== Sample session === * go to our created testing directory and start ''dumm'': {{{
cd umldir
ipsec dumm
}}} * create and start hosts alice and bob, each with an interface: {{{
  1. guest
    guest# create
    guest name: alice
    kernel image: linux-
    master filesystem: master
    amount of memory in MB: 128
    guest 'alice' created
    guest/alice# start
    guest 'alice' is booting
    guest/alice# addif
    interface name: eth0
    guest/alice# back
    guest# create
    guest name: bob
    kernel image: linux-
    master filesystem: master
    amount of memory in MB: 128
    guest 'bob' created
    guest/bob# start
    guest 'bob' is booting
    guest/bob# addif
    interface name: eth0
    guest/bob# back
    guest# back #
    }}} * create a bridge and attach guests interfaces: {{{
  2. bridge
    bridge# create
    bridge name: br0
    bridge 'br0' created
    bridge/br0# addif
    guest name: alice
    interface name: eth0
    bridge/br0# addif
    guest name: bob
    interface name: eth0
    bridge/br0# back
    bridge# back #
    }}} * interface manipulation on netlink is not done yet, so do it manually: * on master: {{{
    ifconfig alice-eth0 up
    ifconfig bob-eth0 up
    ifconfig br0 up
    }}} * on alice: {{{
    ifconfig eth0 up
    ifconfig eth0 netmask
    }}} * on bob: {{{
    ifconfig eth0 up
    ifconfig eth0 netmask