Having "real" and "private" IPs work together on one hub

Having "real" and "private" IPs work together on one hub

Post by Eric Macaule » Wed, 17 Jan 2001 15:04:25



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Having "real" and "private" IPs work together on one hub

Post by Joerg Morbitze » Wed, 17 Jan 2001 17:07:04



> Here's my setup:
>         Cable modem connected to the uplink port of an 8-port hub
>         4 machines with real IPs (bought for extra from the cable company)
>         connected to the same hub as the cable modem
>         1 machine using a "private" 192.168.0.1 IP also connected to this hub

> When I try to telnet to the "private" machine at 192.168.0.1 from one of
> my machines that has a real IP, I get a host unreachable error message.
> I also get the same when I try to telnet from my "private" machine to one
> of my machines with a real IP.  Is it possible via adjusting the routing
> tables (all machines are running linux) to make it so I could telnet
> freely from one machine to another on my local network here?  Or do I
> have to add a second a network card on to one of my machines and have a
> separate hub for the "private" portion of my network?

> Any info/references would be greatly appreciated.

Just plugging a cable into the same hub does not help.
Machines can only "see" each other if they are in the
same network range. In your case the official ip addresses
you got from your ISP are different of your private ip
address 192.168.0.1. Best would be to buy another ethernet
card, put them into a box with an official ip address and
set the ip address for example to 192.168.0.2. Then these
two machines can "see" each other.

It would help you to read some kind of networking howto.

Kind regards, Joerg.

 
 
 

Having "real" and "private" IPs work together on one hub

Post by James Knot » Wed, 17 Jan 2001 22:40:01


Since your real and private addresses have different network
addresses, your computers don't know what to do.  You can
get around this, by assigning a private alias IP address to
the computers with the real IPs.


> Here's my setup:
>         Cable modem connected to the uplink port of an 8-port hub
>         4 machines with real IPs (bought for extra from the cable company)
>         connected to the same hub as the cable modem
>         1 machine using a "private" 192.168.0.1 IP also connected to this hub

> When I try to telnet to the "private" machine at 192.168.0.1 from one of
> my machines that has a real IP, I get a host unreachable error message.
> I also get the same when I try to telnet from my "private" machine to one
> of my machines with a real IP.  Is it possible via adjusting the routing
> tables (all machines are running linux) to make it so I could telnet
> freely from one machine to another on my local network here?  Or do I
> have to add a second a network card on to one of my machines and have a
> separate hub for the "private" portion of my network?

> Any info/references would be greatly appreciated.

> Regards,
> Eric Macauley


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Having "real" and "private" IPs work together on one hub

Post by David Efflan » Thu, 18 Jan 2001 13:27:37



>Here's my setup:
>    Cable modem connected to the uplink port of an 8-port hub
>    4 machines with real IPs (bought for extra from the cable company)
>    connected to the same hub as the cable modem
>    1 machine using a "private" 192.168.0.1 IP also connected to this hub

>When I try to telnet to the "private" machine at 192.168.0.1 from one of
>my machines that has a real IP, I get a host unreachable error message.
>I also get the same when I try to telnet from my "private" machine to one
>of my machines with a real IP.  Is it possible via adjusting the routing
>tables (all machines are running linux) to make it so I could telnet
>freely from one machine to another on my local network here?  Or do I
>have to add a second a network card on to one of my machines and have a
>separate hub for the "private" portion of my network?

If you are sure that the boxes with private IPs are secure, I would think
you could just add this to the boxes with internet IPs:

/sbin/route add -net 192.168.0.0 dev eth0

But maybe you need an alias IP on the nic and/or a -host route first.  But
it would be safer to use a separate nic for the private LAN so you could
MASQ it for internet access.

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