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 experimental and in development (see source:src/dumm).
Along with the dumm library, two frontends are currently usable:

• A graphical GTK client
• A console client with Ruby bindings to script scenarios in Ruby

The graphical client is incomplete. It is missing:

• Removal of added switches
• Disconnecting guests from switches
• Scenario management

The Ruby console client also misses a surrounding testing infrastructure which
will be built with ruby in the near future.

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 recommended
    • FUSE enabled
    • support for TAP devices
  • Userland:
    • libstrongswan
    • libbridge from bridge-utils
    • using the GTK client:
      • GTK+2 with developement headers
      • Gnome VteTerminal with developement headers
    • using the Ruby client:
      • Ruby 1.8 with developement headers
      • IRB
• Guest:
  • Kernel:
    • hostfs
    • tuntap networking
    • our extended mconsole exec patch (see source:src/dumm/patches)
  • Userland:
    • ip from iproute2

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
      args       - additional arguments to pass to guest, such as memory configuration
      pid        - PID file if guest is running, handy to attach gdb to kernel
      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
  templates/     - contains all scenario templates
    test1/       - a scenario folder
      diff/      - copy-on-write overlays for each guest's union folder
        alice/   - COW for alice
        bob/     - COW for bob

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 ruby1.8-dev irb1.8
  

• install libbridge manually:

  git clone git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/bridge-utils.git
  cd bridge-utils
  autoconf
  ./configure
  cd libbridge
  gcc -fPIC -c libbridge_devif.c libbridge_if.c libbridge_init.c libbridge_misc.c
  ar rcs libbridge.a libbridge_devif.o libbridge_if.o libbridge_init.o libbridge_misc.o
  ranlib libbridge.a
  install libbridge.a /usr/local/lib
  install libbridge.h /usr/local/include
  

• Build and install strongSwan from Git sources:

  git clone http://git.strongswan.org/strongswan.git
  cd strongswan
  less HACKING
  ./autogen
  ./configure --enable-dumm [other options]
  make
  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. SKAS3 is not required, but guests run much faster with SKAS3 enabled on the host.

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 "my config": .config):

  wget http://kernel.org/pub/linux/kernel/v2.6/linux-2.6.27.tar.bz2
  tar jxvf linux-2.6.27.tar.bz2
  cd linux-2.6.27
  make mrproper
  wget -O - http://trac.strongswan.org/browser/trunk/src/dumm/patches/mconsole-exec-2.6.27.patch?format=txt | patch -p1
  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.

• Using the irdumm ruby client

  sudo ipsec irdumm
  irb> sun = Guest.new("sun", "path/to/linux-2.6.27/linux", "path/to/master/", "mem=64M con0=xterm")
  irb> sun.start
  irb> sun.exec("echo sun > /etc/hostname")
  irb> sun.add("eth0").connect(Bridge.new("br0")).add("192.168.0.1")
  irb> sun.exec("ifconfig") { |line| puts line }
  irb> quit
  

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