BOOTP and fai-install server on different machines

[Paul Lussier]

In a message dated: Wed, 19 Jun 2002 08:17:07 +1000
Andrew Pollock said:

>I believe you can run two DHCP servers on the same segment, I have. I had a
>Windows based DHCP server serving the normal pool and a Linux DHCP server with
>static leases in it (no pool). The two coexisted fine. I'm not sure if this was
>more by good luck than good management though.

You can definitely do this, however, you really should make sure that 
the pool of addresses, whether dynamically allocated or statically 
assigned are separate for each server.

So, for instance, if you want to serve the 192.168.1.0 subnet from 2 
servers, you can evenly split the address between the 2: 

	server 1	192.168.1.0-127
	server 2	192.168.1.127-255

The problem is that when you want specific clients to only boot using 
1 of the 2 servers.  In this case, you must ensure that those special 
clients are known by both servers, and that only one server will 
assign an address to them.  This can be done by configuring one 
server to answer these client's requests and the other to ignore the 
requests using the client's MAC address.

If you were to have one server providing an address to "unknown clients"
(i.e. the server just answers any request and dynamically assigns an 
address from a range) and the other server has is configured only 
server "known clients" (i.e. each client is statically assigned an 
address based on MAC address) then you could very well encounter a 
race condition problem where the first server to answer the client's 
request is the wrong server.

This can happen because DHCP is a broadcast protocol where the 
request is blasted out to the entire subnet.  The first server to 
answer wins, and that's the information the client takes.  So it is a 
very real possibility that you could boot a client expecting it to 
perform an FAI, yet the system just attempts to boot normally.  
Depending upon the state of the OS on the system, and the mechanism 
you're booting with (floppy, PXE, etc.) you may or may not have a 
a properly booted system after the DHCP assignment.

HTH,
-- 

Seeya,
Paul
----
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   but I'm really actively waiting for all my problems to go away.

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