How to add a second DHCP server in a network to use PXE boot without conflict with the first one ?

Hi all,

I need to boot a computer with a PXE compliant card from network.
To do it, I use a ISC DHCP server V3 and a TFTP server. (Linux distribution
used is Debian)

The problem is that there is another DHCP server on the network, and I have
no right on it. This DHCP server is configured to respond to a DHCP request
from my computer when I boot it normally. (ie: From the hard drive)

I would like to configure the DHCP server I installed for booting, to
respond only to DHCP request from PXE client and not from a normal DHCP
client.

Here is my dhcpd.conf file, I would like to know what can I do to prevent
the DHCP server to respond to none PXE client requests ?

Thanks by advance.
Hilaire Verschuere.


# /etc/dhcp3/dhcpd.conf

not authoritative;
ddns-update-style none;

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;


subnet 10.1.11.0 netmask 255.255.255.0 {

class "pxeclients" {
match if substring (option vendor-class-identifier, 0, 9) = "PXEClient";
option vendor-class-identifier "PXEClient";
vendor-option-space PXE;
option PXE.mtftp-ip 0.0.0.0;

next-server 10.1.11.99;
}

host phobos {
hardware ethernet 00:0c:29:23:ab:1a;
fixed-address 10.1.11.93;
filename "pxelinux.0";
}
}

On Tue, 22 Nov 2005 11:16:06 +0100, HIL wrote:

[snip]
> Here is my dhcpd.conf file, I would like to know what can I do to
prevent
> the DHCP server to respond to none PXE client requests ?

[snip]

> host phobos {
> hardware ethernet 00:0c:29:23:ab:1a;
> fixed-address 10.1.11.93;
> filename "pxelinux.0";
> }
> }


I did something similar with etherboot once, it seems to me that this
should suffice. Just add the MAC-adresses it should respond to and it will
ignore any other.

Try running "tail -f /var/log/messages" while DHCP-server is running.


Tomas

Hi,

Yes, this configuration works and my machine boot correctly.
The problem is that I don't want my dhcp responds to a request from the same
machine (ie with the same mac address) if it is not from PXEclient, in
other words if it is a normal dhcp request from dhclient by exemple.

For the moment, it responds to all dhcp requests (PXEClient, dhclient,...),
does anyone know how I can change my configuration file dhcpd.conf to
filter only PXEClient ?

Thanks by advance.
Hilaire Verschuere

May be, someone knows where I can find any information about it ?

Hilaire.

In article <4395a888$0$29625$(E-Mail Removed)>, (E-Mail Removed) says...
>
> May be, someone knows where I can find any information about it ?

I recently learned all about PXE boot when getting Ghost backups to work
over the network using PXE Boot. So I can't answer your exact question
but I can provide some other info...

My understanding is that the PXE Client "is" a DHCP client but with a slight twist.
The client includes an option that says it's a PXE client. Below is how the option
appears in WireShark:
Option: (t=60,l=32) Vendor class identifier = "PXEClient:Arch:00000:UNDI:002001"

So you would need the DHCP server to support recognizing this option or perhaps ignoring
DHCP requests that have that option. I don't know if this is possible.

PXE is designed to work with multiple DHCP servers sending information so
I believe it's possible for both a PXE server and DHCP server to co-exist.
That is one configuration I've tested.

You should see http://en.wikipedia.org/wiki/Dynamic...ation_Protocol
for a description of how DHCP works because PXE is a variant on DHCP.
The following http://www.3com.com/other/pdfs/infra.../en_US/pxe.pdf describes
how PXE works.

Again, these aren't answers but hopefully they'll help you find out more about
how it works so you can see if DHCP servers can be configured to filter these
PXE requests.

Regards,
Patrick Steranka