Networking/routing question

Kayvan Aghaiepour Sylvan (kayvan@sylvan.com)
22 Dec 1998 08:27:08 -0000


I'm answering my own question, since I found the answer by trial and
error:

> I've got a small block of IP addresses assigned to me by my
> ISP. Historically, I've used PPP to connect all my machines together
> (PPP over direct serial links!) and that way each of them have their
> own IP address. I use my Linux box as the gateway and firewall out
> to the net.

> For example, I have:

> [Win95 Machine] [Linux]
> IP: 204.153.195.5 <--- PPP direct link ---> 204.153.195.1 <--- PPP ---> ISP

> I've recently put in a local ethernet setup between all my machines,
> so now, in addition to the above setup, I have:

> [Win95 Machine] [Linux]
> IP: 192.168.0.2 <--- Ethernet -------------> 192.168.0.1

> What I want to know is how to eliminate the direct link between the
> Win95 machine and my Linux box and still let the Win95 machine have
> its own assigned IP address.

> Something like this:

> [Win95 Machine] [Linux]
> IP: 204.153.195.5 <----- Ethernet ---------> 192.168.0.1
> ^
> |
> v
> 204.153.195.1 <--- PPP ---> ISP

> In the last scenario, ideally my Linux box would transparently move
> traffic destined to/from the Win95's static IP to the ethernet IP
> assigned to it for my local network.

> How can I set this up?

The answer turned out to be surprising to me. I found out that I can
set up my eth0 interface with the same IP address as my ppp0 interface
(my Linux router's IP address).

Then, adding a network route to make sure all the traffic to my local
network goes through eth0 is all I need.

The other machines on my network then just access the network with
their own assigned IP numbers on the eth0 interface.

So the picture looks like this:

[Win95 Machine] [Linux]
IP: 204.153.195.5 <--- Ethernet ---> eth0 = 204.153.195.1
ppp0 = 204.153.195.1 <-- PPP --> My ISP

I was under the impression that different interfaces on the same
machine need to have different IP numbers, but this setup seems to
work perfectly. Any comments?

---Kayvan

-- 
Kayvan Aghaiepour Sylvan |Sylvan Associates         | Proud Dad of:
kayvan@Sylvan.COM        |http://www.isp.net/~kayvan| Katherine Yelena (8/8/89)
(408) 978-1407 PGP OK    |Ask me about Avatar.      | Robin Gregory (2/28/92)
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