Network, routers, DHCP and PXE

[Manolis Kiagias]

Svein Halvor Halvorsen wrote:
> Hi, list!
>
>
> I have a private home network, on an ADSL2+ connection to the
> internet. The home network is behind NAT, all automatically set up
> by the router/dhcp server/wlan access point/adsl modem that I got
> from my ISP. It's a Thomson SpeedTouch 585 router.
>
> Now, on this network, most of the computers get their IP by means of
> DHCP. Except our home audio server, which have a hard coded ip
> address in rc.conf, set to something within the range of the dhcp
> server (10.0.0.2-10.0.0.253). The server seems to pick this up, and
> don't give that address away to someone else.
>   

You may also want to ensure that the router will never allocate your 
static IP address to someone else.
Look at the DHCP router settings either for DHCP scope (set it to 
narrower values, and use a static IP outside the range) or for something 
like exceptions / exclusion where you can mark a specific IP that DHCP 
will never assign.
> I've tried using other addresses outside this range, like 10.0.1.1,
> but that doesn't work. All network access is lost when I do that.
>   

 10.0.1.1 is a different network (I assume your netmask is 
255.255.255.0, but check your router or your clients)

> Now, on my local network I'd like to put a diskless machine. As I
> understand it, my DHCP server needs to tell the client about the
> "filename" and a "next-server" to use. I don't think I can setup the
> Thomson router to do this. All the instruction I can find online
> advises me to install a DHCP server on the same machine that serves
> the pxe boot image. But if I do that, I'll get two DHCP servers on
> my local network. Is that ok? Will there be a race condition, when a
> client asks for an IP address?
>   

You will have to shutdown the router's DHCP. Probably disable it 
permanently and assign this function to a machine.
The DHCP of the router also sends you the following information (besides 
IP address):

- DNS Server(s): Either the ones used by your ISP (consult its website) 
or its own address (i.e. 10.0.0.1). Most routers send their own address 
as a DNS server and perform the resolution by sending your request to 
ISP servers.
- Gateway address: This is always the router's local IP address (i.e. 
10.0.0.1)

If you setup your own DHCP server, make sure it is set to send this info 
as well. (These are commonly known as DHCP options)