A DHCP server is needed to assign an IP address to nodes during and after installation. It configures a basic network on the nodes, and informs them on which computer will be the tftp server. You can find documentation of how to set up a DHCP server with PXE options at: http://people.mandriva.com/~aginies/doc/pxe/ch04.html

To quickly set up a DHCP server, just check file /etc/clusterserver.conf, in section DHCP, and launch setup_dhcpdconf_server. This will configure the /etc/dhcpd.conf file. The setup_add_nodes_to_dhcp script exists to catch MAC address of nodes, and with parameter -n numberof_nodes, will update the /etc/dhcpd.conf file after it sees numberof_nodes new MAC addresses.

You can find more information on how to set up a DHCP here: http://www.tldp.org/HOWTO/mini/DHCP/index.html

/etc/dhcpd.conf example

ddns-update-style none;
allow booting;
allow bootp;

# Your dhcp server is not master on your network !
#not authoritative;
# Your dhcpd server is master on your network !
#authoritative;
not authoritative;

#Interface where dhcpd is active
#DHCPD_INTERFACE = "eth0";

# Definition of PXE-specific options
# Code 1: Multicast IP address of bootfile
# Code 2: UDP port that client should monitor for MTFTP responses
# Code 3: UDP port that MTFTP servers are using to listen for MTFTP requests
# Code 4: Number of secondes a client must listen for activity before trying
#         to start a new MTFTP transfer
# Code 5: Number of secondes a client must listen before trying to restart
#         a MTFTP transfer

# define Option for the PXE class
option space PXE;
option PXE.mtftp-ip code 1 = ip-address;
option PXE.mtftp-cport code 2 = unsigned integer 16;
option PXE.mtftp-sport code 3 = unsigned integer 16;
option PXE.mtftp-tmout code 4 = unsigned integer 8;
option PXE.mtftp-delay code 5 = unsigned integer 8;
option PXE.discovery-control code 6 = unsigned integer 8;
option PXE.discovery-mcast-addr code 7 = ip-address;

#Define options for pxelinux
option space pxelinux;
option pxelinux.magic      code 208 = string;
option pxelinux.configfile code 209 = text;
option pxelinux.pathprefix code 210 = text;
option pxelinux.reboottime code 211 = unsigned integer 32;
site-option-space "pxelinux";
# These lines should be customized to your setup
#option pxelinux.configfile "configs/common";
#option pxelinux.pathprefix "/pxelinux/files/";
#filename "/pxelinux/pxelinux.bin";
                                
option pxelinux.magic f1:00:74:7e;
option pxelinux.reboottime 30;
#if exists dhcp-parameter-request-list {
# Always send the PXELINUX options
#       append dhcp-parameter-request-list 208, 209, 210, 211;
#       append dhcp-parameter-request-list 208,211;
#                                       }

#Class that determine the options for Etherboot 5.x requests
class "Etherboot" {

#if The vendor-class-identifier equal Etherboot-5.0
match if substring (option vendor-class-identifier, 0, 13) = "Etherboot-5.0";

# filename define the file retrieve by the client, there nbgrub
# our tftp is chrooted so is just the path to the file
filename "/etherboot/nbgrub";

#Used by etherboot to detect a valid pxe dhcp server
option vendor-encapsulated-options 3c:09:45:74:68:65:72:62:6f:6f:74:ff;

# Set the  "vendor-class-identifier" field to "PXEClient" in dhcp answer        
# if this field is not set the pxe client will ignore the answer !
option vendor-class-identifier "Etherboot-5.0";

vendor-option-space PXE;
option PXE.mtftp-ip 0.0.0.0;

# IP of you TFTP server
next-server 12.12.12.253;
}


# create the Class PXE
class "PXE" {
# if the "vendor-class-identifier" is set to "PXEClient" in the client dhcp request
match if substring(option vendor-class-identifier, 0, 9) = "PXEClient";

# filename define the file retrieve by the client, there pxelinux.0
# our tftp is chrooted so is just the path to the file
# If you prefer use grub, use pxegrub compiled for your ethernet card.
#filename "/PXEClient/pxegrub";
filename "/X86PC/linux/linux.0";

# Set the  "vendor-class-identifier" field to "PXEClient" in dhcp answer
# if this field is not set the pxe client will ignore the answer !
option vendor-class-identifier "PXEClient";

vendor-option-space PXE;
option PXE.mtftp-ip 0.0.0.0;

# IP of you TFTP server
next-server 12.12.12.253;
}
# Tags uses by dhcpnode and setup_add_nodes_to_dhcp
# TAG: NODE_LIST_ADMIN_BEGIN
host node1 {
    hardware ethernet 00:02:b3:3f:78:8c;
    fixed-address node1;
}
# TAG: NODE_LIST_ADMIN_END

# TAG: NODE_LIST_COMPUTE_BEGIN

# TAG: NODE_LIST_COMPUTE_END

# TAG: MY_ADMIN_BEGIN
subnet 12.12.12.0 netmask 255.255.255.0 {
  option subnet-mask 255.255.255.0;
  option routers 12.12.12.253;
  default-lease-time 288000;
  max-lease-time 864000;
  option domain-name "guibland.com";
  option domain-name-servers 12.12.12.253;
# Used by clusterautosetup-client to find its server
  next-server 12.12.12.253;

  pool {
  range 12.12.12.1 12.12.12.128;
  }
}

# TAG: MY_ADMIN_END

# TAG: MY_COMPUTE_BEGIN

subnet 192.168.200.0 netmask 255.255.255.0 {
  option subnet-mask 255.255.255.0;
  default-lease-time 288000;
  max-lease-time 864000;
  option domain-name "mandriva.com";
  option domain-name-servers  192.168.100.11;

  pool {
    deny members of "PXE";
    range 192.168.200.10 192.168.200.99;
  }
}

# TAG: MY_COMPUTE_END
}