OT: Linking a new network to the LAN

[Bill Campbell]

On Wed, Dec 28, 2011, Boaz Bezborodko wrote:
>I figured someone here would now how to resolve this problem.
>
>I have a machine using an Allen-Bradley PLC that is addressed to 
>10.1.1.x while my LAN is 192.168.1.x.  I need to let the machine's 
>designer have access to the PLC via the internet in order to make a 
>small change to the program.  I have set up a VPN server connection on 
>my computer for him to access the network, but he still can't access the 
>PLC.  His A-B support told him that I would need to add a router to the 
>machine and set it up to look at my network as a WAN while using port 
>forwarding to access the PLC.
>
>It seems to me that there should some other way to get access to the PLC 
>using either my router or my Linux server to do this.

My first option would be to change the IP address/network on the
PLC box to one on the 192.168.1.0/24 LAN (really I wouldn't use
either 192.168.0.0/24 or 192.168.1.0/24 as these can cause some
Really Interesting routing issues if people log in via a VPN from
a network where they've been too lazy/ignorant to reassign the
network from the vendor's defaults).

If the VPN server on the network is on a Linux machine, it's easy
to set up an IP alias on its LAN interface to talk on the
10.1.1.0/24 net block.  This is possible on non-Linux systems,
but it's been a while since I played that game.  If the VPN
server is a commodity router box with limited capabilities, you
can set a static route on it to point to a Linux box or other
that can talk to the PLC network.  Worst case, install another
NIC in a machine on the LAN that can talk to this network.  NICs
are much cheaper than routers.

Bill
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