PXE - Preboot eXecution Environment - Setting Up DHCP

PXE - Setting Up DHCP

For fun in one of the labs I set up my own PXE server and made notes about the problems that I encountered in doing so. If you aren't really sure what PXE is, a decent description exists at wikipedia. In a nutshell the client sends/ broadcasts a request for a Network Bootstrap Path. The server authenticates that the request comes from a legit source and, if so, sends the path to the client. The client then executes the path and installs the given OS.

I am running an older 64 bit Dell Poweredge with Ubunutu 12.04.

To get started you will want to do a little bit of reading if you haven't already. I found the following two posts to most informative:

https://help.ubuntu.com/community/PXEInstallServer
http://blog.alainodea.com/en/ipxe-smartos

So do a little bit of background reading if you haven't yet, but odds are you already looked at those which is why you are here. If you already have DHCP configured skip those parts.

Got DHCP?

After I read these through a few times, I noted that I had several constraints. I needed at least one box to be the client. Several desktops exist in the lab that will likely serve (they did not). Additionally when I started, DHCP in the lab was broken so I had to see if I could get that resolved too.

You'll need:

isc-dhcp-server which is the dhcp server and handles networking. You'll also need tftpd-hpa which is Trivial File Transfer Protocol and it handles the transfer of the OS from the server to the client.

$> sudo apt-get install isc-dhcp-server 
$> sudo apt-get install tftpd-hpa   

Create or edit  /etc/default/tftpd-hpa with the following content (may already exist):

    # /etc/default/tftpd-hpa
    TFTP_OPTIONS="--secure --verbose"
    TFTP_USERNAME="tftp"
    TFTP_DIRECTORY="/var/lib/tftpboot"
    TFTP_ADDRESS="0.0.0.0:69"

Most of it was already there, but I added verbose.
   
$> sudo service tftpd-hpa restart
     

Editing dhcpd.conf

Now create or edit /etc/dhcp/dhcpd.conf

with the following content (adjust the subnet, range and domain-name as required):

    server ip:     1xx.2xx.2xx.2xx  // this will be same as 'next-server'
    gateway:    1xx.2xx.2xx.1xx
    subnet:        1xx.2xx.2xx.1xx
    netmask:    255.255.255.xxx
    filename:    determined by OS we will be loading basically.

So you'll need the information about your gateway, subnet and netmask. I found that information by asking around. So the file will look something like:


#----------------------------------------------------
subnet 1xx.2xx.2xx.1xx netmask 255.255.255.xxx {
  pool {
    range 1xx.2xx.2xx.2xx 131.2xx.2xx.2xx;  
    next-server 1xx.2xx.2xx.2xx;
    filename="pxelinux.0"
  }
}
#-----------------------------------------------------

But since no one was going to be authoritative about Dynamic Host Configuration Protocol in the labs, I asked if I could and so got permission. Now the file looks like this:

#-----------------------------------------------------
 18 # If DHCP server is the official DHCP server for the local
 19 # network, the authoritative directive should be uncommented.
 20  authoritative;
 :
 :
 34 subnet 1xx.2xx.2xx.1xx netmask 255.255.255.2xx {
 35 # option definitions common to all supported networks...
 36 # subnet mask advises client to use that mask
 37 # broadcast-address: where all clients receive messages from
 38 # option routers tells the client that the gateway is there
 39 default-lease-time 600;
 40 max-lease-time 7200;
 41 option subnet-mask          255.255.255.2xx;    # /27 - cidr
 42 option broadcast-address    1xx.2xx.2xx.2xx;    # town crier
 43 option routers              1xx.2xx.2xx.1xx;    # the gateway
 44 option domain-name-servers  1xx.2xx.2xx.2xx;    # DNS server
 45 option domain-name          "foo.bar.org";      # our domain!
 46   pool {
 47     range 1xx.2xx.2xx.1xx 1xx.2xx.2xx.2xx;      # I control
 48     # range 2xx-2xx; if not authoritative so I can be less
 49     # controlling :)
 50     next-server 1xx.2xx.2xx.2xx;                # pxe server
 51     filename="/pxelinux.0";                     # pxe loader
 52   }
#----------------------------------------------------------------------------------
The pxe server is the next-server and is presumably your server that you control. The client is the one who (assuming you have a PXE enabled machine - check the bios) when you hit f12 gets an ip now from your dhcp server and then is provisioned by the server with the OS you select. You can test what you have so far by plugging in a box and seeing if you get assigned an IP address.

Next Up: LET'S PXE!