We have a problem booting a PXE client from a different subnet than
the PXE server.
We use Lucent's QIP for providing DHCP information to the client and
3Com Boot Services as PXE server. Client, QIP DHCP and PXE Server are
all on a different subnet.

As recommended in the PXE Specification, we set DHCP option 43 on QIP
thus instructing the client to go directly (unicast) to the PXE Server
to get extended DHCP information (bootfilename, TFTP path, etc.)

The problem is that the client just won't boot. It gets the IP address
and everything from the QIP DHCP but then starts to talk to the PXE
server and finally hangs with the following error:

PXE-E78: Could not locate boot server.

We've captured incoming/outgoing traffic from the client and the
strange thing we see is that it queries the PXE server on port 4011
*from* port 4011 instead of 68 (bootclient)
The PXE server replies to the client with the correct information
(bootfilename, path, etc.) *but* to client port 4011.
This "ping-pong" occurs 4 times and the client finally hangs with
error PXE-E78

Do you have any idea of what is happening ? Do we miss something ?

Thank you in advance,