Subject: [dhcwg] Design Issue

From: "Huma Hakim" <[email-masked]>
Date: Thu, 27 Sep 2001 15:41:14 +0000

Hello

I have a set-up in which one or more host machines may be connected to my 
dhcp server through a box X( This box X routes along with serving  other 
functions too like sending packets from the host machines to my central 
station where the dhcp server is situated). Box X as well as these host 
machines may (optional) also connected to another LAN through another router 
A which cannot be configured by me as it does not belong to me.

-----------------          |---------|      |-Host m/c
|Central Station |---------|  Box  X |------|
|DHCP Server     |         |         |      |-------RouterA----LAN
-----------------          |---------|      |       (optional)  (opt)
                |                           |-Host m/c
                |
                |
                |
                |
                |----------|---------|      |-Host m/c
                |          |  Box Y  |------|
                |          |         |      |-------Router B----LAN
                |          |---------|      |       (optional)  (opt)
                |                           |-Host m/c
                |
                |
                |
                |---------------
                |
                |
                |
                |---------------
                |
                |
My job is to assign an IP address and subnet mask at the very least to my 
box A as well as to all the host machines that may be connected to my box A 
through a DHCP server that my box A talks to at the central repository. All 
the host machines connected to my box A communicate to my central repository 
to obtain data/information via my box A. I could have a number of such boxes 
along with their respective host machines that communicate simultaneously to 
my central station.All these boxes have to have different subnets coz 
essentially they are all routers, and no two routers can belong to the same 
subnet.
For these boxes/host machines groups to talk to each other , packets have to 
be routed by my central repository.The message is first sent to the central 
side and then a router there will route the packet and send it back to the 
appropriate box. Hence if more than one box has the same subnet, the router 
on the central side will not know which interface to send the packet to in 
order to reach a particular box
Cable modems and DSL might have a similar problem but im sure they dont care 
if their subnets overlap coz it doesnt affect their functionality

The different scenarious are:
1. stub network
2.Networks with public and well as private addressing(may have some 
implementation like NAT) or i might have to use something like that
3. Networks which might have public and private addressing as well as be 
multihomed.
The main criteria is that the DHCP server should be on our the central 
respoitory side. i.e. it should provide dhcp addressing
Any of the boxes( could be called routers as in routing traffic to the 
central station) or host machines connected to our box should be able to ask 
for an address if it needs one.
If the ip address we assign to either a box or a host machine is on a 
different subnet from the LAN to which they are attached to, an address 
entry (subnet entry) in the router table (maybe use RIP ??) may have to be 
done
The problem is what subnet do i assign to this box or host machine i.e. on 
what basis do i have entries in my dhcp server? coz they cannot be based on 
hardware addresses as a host machine can have just abt any h/w address which 
i have no control over..
Aim is to give ip's and subnet masks to ppl who ask my server but how do i 
relate all of them
My dhcp client software which will reside on my box needs to act like a dhcp 
client when it is asking for a subnet and ip address for itself and as a 
relay agent when it is asking for a subnet and ip address for the host 
machines attached to it. So obviously till my box does not come up and get 
initialized it cannot act like a relay agent(as it has no idea what its 
configuration is till it contacts my dhcp server)

I hope i was able to put my problem across.. my aim is to find some 
architecure to make this design possible. I would be very grateful if 
someone could help me out or point me to some relevant material
One possible solution was to send the MAc address of my box as the agent 
circuit id sub option in the dhcp agent information option and let the MAC 
addresses of the host machines act as the agent remote id suboption but I am 
sure a better solution exist

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