Problem related with Subnetting

From: Rajat (myself_rajat_at_yahoo.com)
Date: 12/07/04 

Date: 7 Dec 2004 02:21:42 -0800

I was getting some problem while posting a follow-up message. So here
starting a new thread.

Sorry I think I couldn't explained my problem well. Let leave all
issues, and concern only with closer proximity problem.
So now we want to know whether 2 clients are behind the same corporate
connection or not. Moreover they are able to communicate to each other
directly or not.

Now we have to decide, where we have to find this thing, either at
conference server side or at one of the client side.

So at the server side if we see that for both client the host IP
address is same(address block provided by the ISP) then we can make
out that both are behind the same subnet(corporate connection).
Now, internally that subnet has 2 possible scenerios,

(1). It may have a single big LAN, if those 2 host exist in that same
LAN.

(2). The subnet is divided into multiple LANs(say for each floor). And
both clients exist in
different LANs. Say one in LAN-1 and another in LAN-2.

So now we have two issues,

(a). Recognize the client's corresponding LANs.
(b). Then find whether they are able to communicate directly or not.

Now assume that conference server can provide the clinet-2's local ip
address to client-1, that it can pick from the client side only, by
filling a informational structure.

So for case (1), client-1 can make out condition (a) by ANDing the
both IP address with subnet mask, and comparing them. For condition
(b) client-1 can ping the client-2.

Now the only problem occurs with case (2), How a client can send some
data to other client, I mean to which address, if it belongs to a
different address space or different LAN, but in the same subnet or
corporate connection.
Actually I have a configuration here, in that, from DSL modem/router
we connect a router/switch and make a LAN of address space 10.0.0.X,
whose address limit will vary from 10.0.0.2 to 100, where 10.0.0.1 is
the address of the router itself. Now we again create a LAN of
20.0.0.X, by using a another router, which will have its WAN address
as 10.0.0.101 and conncet it to one of the port of 10.0.0.X router. So
the problem is, we are able to ping any host of LAN 10.0.0.X from any
host of LAN 20.0.0.X. But we are not able to ping in reverse
direction. So the host of 20.0.0.X LAN are able to host of 10.0.0.X
LAN but vice versa it is not true.
Can any one point out why??

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