[LUNI] Running 2 networks on same physical wire

[Carey Tyler Schug]

I assume the RJ45 outlet upstairs is connected to an RJ45  outlet in the 
basement.

I assume you actually have:

  computers on network 1--+
                          |
  computers on network 1--+
                          |
             +--router 1--+                                       
+--computer on network 1
             |                                                    |
ISP router---+                            >-RJ45-------RJ45-<<----+ 
                                 
             |                                                    |
             +--router 2--+                                       
+--computer on network 2
                          |
  computers on network 2--+
                          |
  computers on network 2--+
                         

Where each set of vertical bars & pluses is one switch, and network 1 
and network 2 are different subnets.

Assuming all computers and routers are trusted and will not try to steal 
each others traffic, all you need is one more switch connected to each 
network in the basement and to the RJ45 port:

  computers on network 1--+    
                          |
  computers on network 1--+
                          |
                          +-----+
                          |     |
             +--router 1--+     |                                 
+--computer on network 1
             |                  |                                 |
ISP router---+                  +-------->>-RJ45-------RJ45-<<----+ 
                                 
             |                  |                                 |
             +--router 2--+     |                                 
+--computer on network 2
                          |     |
                          +-----+
                          |
  computers on network 2--+
                          |
  computers on network 2--+
                         
Each computer will ignore the other network (wrong subnet) and the 
switches at each end will direct traffic to only the computers who want it.

If the switches are smart (you can log on to them from the network), 
each will be defined on one of the two networks, and you will not be 
able to log on from the other network, or at least not easily.  I guess 
if you had routes on you could loop through the basement and come back 
to log on to the switch.

The cleanest way, possible with Cisco and some other switches, would be 
to have ONE switch at each location (plus the one associated with the 
ISP router), and a "trunk" between them, using VLANs, then no computer 
will ever see any traffic from the other network.

  computers on network 1-+
                         |
  computers on network 1-+
                         |
             +--router 1-+                                     
+-1--computer on network 1
             |           |                                     |
ISP router---+           +-T--------->>-RJ45-------RJ45-<<---T-+ 
                                 
             |           |                                     |
             +--router 2-+                                     
+-2--computer on network 2
                         |
  computers on network 2-+
                         |
  computers on network 2-+

where "--1-+" indicates that port is assigned to vlan #1, "--2-+" 
indicates that port is vlan #2, and "--T-+" indicates that port is a trunk.

====================

Of course, if these are standard 10/100 MB (not gigabit or 100T4) each 
network only uses 4 wires, so you could build a custom cable to connect 
each end of the RJ45 jacks to the two networks, and eliminate the 
switches at each end, and get bigger throughput also.  You seemed to 
state only two computers upstairs, if you added more, you would still 
need switches upstairs.  I see somebody else has suggested this... 
easier variations than making a male to two female adapter include

(1) Take one ethernet cable, cut it in half.  Remove a piece of the 
outer covering and select the appropriate 4 wires from each, thread them 
into the piece of cover and crimp them into an RJ45 plug.

(2) get a duplex wall jack and rewire that as two outlets.  I have seen 
these at some $1 stores (well, $1 for the mounting plate, and $1 each 
for jacks, total $4-6 with upstairs and downstairs depending on whether 
you can reuse the present jack).


Jay Strauss wrote:
> Hi,
>
> I need to have 2 computers sitting physically side to side to be on
> different networks.  I only have a single RJ-45 outlet.  The whole
> setup looks like:
>
>             |-Router 1-                            |- Network 1
> ISP--switch-|                --RJ45 outlet--switch-|
>             |-Router 2-                            |- Network 2
>
> The <blank> space between the routers and the RJ45 outlet is on
> purpose, because I don't know what to put in there.
>
> The RJ45 outlet is upstairs, and the routers are in my basement.  I
> can NOT simply move the routers upstairs because there are numerous
> computers hanging off of the routers in the basement.
>
> I'm not sure if what I want to do is possible or what equipment I need
> to get.  Any help/suggestions would be most appreciated.
>
> Thanks
> Jay
>   

-- 
Carey Tyler Schug