Re: Re: DHCP

On Wed, Oct 24, 2001 at 08:46:02PM +0000, Sean Adams wrote:
> 
> Kevin,
> 
> Yep, I understand and I agree, although I'm not entirely sure of all the
> specifics - I was just thinking out loud.
> 
> Step by step then:
> 
> 1. The player sends a UDP packet to the Ethernet broadcast address. What
> IP address should be specified in this packet?  Will Windows deliver it to
> the server application if the IP address is, say 255.255.255.255, or do we
> need to snoop the Ethernet port?  I know if it's an IP packet sent to say,
> 192.168.10.255, we'll get it. But if the player doesn't know the subnet
> address, can it still send a valid IP broadcast?  I guess I'll just
> look at the RFC for DHCP - would have taken me less time that writing
> this question :)

Use 255.255.255.255 to a specific port, and have the server open a 
socket to listen on that port for the broadcast.  Similarly, have
the firmware open a socket and listen for the response, which would
contain the server's IP (and could also contain netmask, gateway, etc.
info, though that should more properly be handled via DHCP on the 
client side).

> 
> 2. The server has figured out in advance which unused/phony IP address it
> will assign. How does it do this?  I guess we would do ARP lookups for
> random IP addresses on our subnet until we find one that's not there - can
> we rely on ping (saves bypassing IP stack), or should we worry about
> machines that respond to arp but not ICMP?
> 

DHCP should be used on the client side before #1 above ever happens.
Then, when the UDP packet to the server arrives, the server knows from
the packet header info which IP the client's been assigned.

> 3. The server then replies to the hardware address that sent the request,
> with the IP destination set to the address we want to assign the player.
> The player gleans it's new IP address and we're done. No subnet mask or
> gateway is needed or allowed in this scheme.
> 

Again, that'd be best handled via DHCP on the client side.


As far as only Windows users wanting this, I can say that I'd love to
have DHCP functionality; I've got near 20 networked devices in my
house, and they're almost exclusively using DHCP and dynamic DNS
functionality for addressing and naming.  Those devices are printers,
wireless access points, console gaming devices, personal video
recorders, FreeBSD servers, OpenBSD servers, Windows desktops, Windows
servers, notebooks, and handhelds.

-- 
Mark C. Langston
[email protected]
Systems & Network Admin
http://www.bitshift.org

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