This is a Dockerfile to build a container running a PXE server, pre-configured to serve a Debian netinstall kernel and initrd.
- Of course you need Docker first!
- Clone this repo and
cd
into the repo checkout. - Build the container with
docker build -t pxe .
- Run the container with
PXECID=$(docker run -d pxe)
- Give it an extra network interface with
./pipework br0 $PXECID 192.168.242.1/24
- Put the network interface connected to your machines on the same bridge
with e.g.
brctl addif br0 eth0
(don't forget to moveeth0
IP address tobr0
if there is one). - You can now boot PXE machines on the network connected to
eth0
! Alternatively, you can put VMs onbr0
and achieve the same result.
The Linux network stack has the notion of master and slave interfaces. They are used in many places, including bridges and bonding (when multiple physical interfaces are grouped together to form a single logical link, for increased throughput or reliability). When using Linux bridges, the bridge is the master interface, and all the ports of the bridge are slave interfaces.
Now is the tricky part: with interfaces like bridges and bonding groups, only the master should have IP addresses; not the slaves. If an IP address is configured on a slave interface, it will misbehave in seemingly random ways. For instance, it can stop working if the interface is down (but the master interface is still up). Or it might handle some protocols like ARP only for packets inbound on this interface.
Therefore, when changing the configuration of an existing interface to place it inside a bridge (or bonding group), you should deconfigure its IP address, and assign it to the master interface instead. I recommend the following steps:
- Check the IP address of the interface (with e.g.
ip addr ls eth0
). Carefully note the IP address and its subnet mask, e.g. 192.168.1.4/24. There can be multiple addresses; in that case, note all of them. - Check if there are special routes going through that interface.
Chances are, that there is a default route, and you will have to
take care of it; otherwise you will lose internet connectivity.
The easiest way is to do
ip route ls dev eth0
. You will almost certainly see an entry withproto kernel scope link
, which is the automatic entry corresponding to the subnet directly connected to this interface. You can ignore this one. However, if you see something likedefault via 192.168.1.1
, note it. - Deconfigure the IP address. In that case, we would do
ip addr del 192.168.1.4/24 dev eth0
. You don't havea to deconfigure the routes: they will be automatically removed as the address is withdrawn. - Configure the IP address on the bridge. In our example, that would
be
ip addr add 192.168.1.4/24 dev br0
. - Last but not least, re-add the routes on the bridge. Here, we
would do
ip route add default via 192.168.1.1
.
If you want to do that automatically at boot, you can do it through
the /etc/network/interfaces
file (on Debian/Ubuntu).
It will look like this (assuming the same IP addresses than our previous example):
auto br0
iface br0 inet static
address 192.168.1.4
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.1
bridge_ports eth0
bridge_stp off
bridge_fd 0
Don't forget to disable the section related to eth0
then!
Left as an exercise for the reader. Check the Dockerfile and rebuild; it should be easy enough.
Yes, if you also change it in the Dockerfile.
Yes, but it will be more complicated. You will have to:
- make sure that Docker UDP can handle broadcast packets (since PXE/DHCP uses broadcast packets);
- make sure that UDP ports are correctly mapped;
- auto-detect the gateway address and DNS server, instead of using the container as a router+DNS server;
- maybe something else that I overlooked.
Let's have a game!
- Burn a boot2docker ISO on a blank CD.
- With that CD, boot a physical machine.
- Run the PXE container on Docker on the physical machine.
- Pull the ubuntu container, start it in privileged mode, apt-get install QEMU in it, and start a QEMU VM, mapping its hard disks to the real hard disk of the machine, and bridging it with the PXE container.
- The QEMU VM will netboot from the PXE container. Install Debian.
- Reboot the physical machine -- it now boots on Debian.
- Repeat steps but install Windows for trolling purposes.