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routing between different subnets/interfaces

Posted on 1999-12-22
Medium Priority
Last Modified: 2010-05-19
What can I do to solve my routing problem stated below?  I don't care whether I have to configure the linux or the NT, so long as it works!

I have an NT 4.0 server using ethernet (, gateway, mask and token ring (, no gateway, mask with RIP service installed and active.

I have an Open Linux 2.3 2.2.10 box using eth0 (206.xxx.xxx.xxx, gateway 206.xxx.xxx.1)which is the 'public' side connected to ISP; eth1 (, no gateway, mask with masquerading installed.

All ethernet stations (10.2.x.x) can utilize the internet as expected and work perfectly; this includes the NT server itself.

All token ring stations (10.1.x.x) can ping ANY other ip on the ethernet side EXCEPT the linux (; and so I believe that is why they CANNOT utilize the internet.  The linux box cannot see any token ring stations.

I have tried adding another default route on the linux pointing to (NT) and that lets ALL stations ping ALL OTHER stations; great except it shuts down access to the internet!

I have tried adding a token ring card to the linux, but as soon as it comes online, it shuts down our WAN router!  Let me know if more info is needed

I hopefully gave this enough of a chunk of points for your trouble :)

Question by:ToddRod
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Author Comment

ID: 2302392
Edited text of question.

Accepted Solution

dcavanaugh earned 1000 total points
ID: 2307663
Have you tried setting the default gateway on the Token Ring stations to

Does the linux box have a static route to the 10.1.x.x network?

route add -net netmask gw eth1

If this does not work, please include the results of the ifconfig and route -n commands from the Linux box.

Expert Comment

ID: 2308473
Things I should have mentioned in the first comment:

Alternative commands for adding the static 10.1.x.x route for the Linux box:

route add -net netmask gw

route add -net netmask eth1

I don't do this often enough to remember which one is precisely right for your situation, but I think the lack of a 10.1.x.x route for the Linux box would cause all of the behavior you mention.  
Assuming you get this to work, you'll have to update your network routing configuration using the appropriate tool for your distribution of Linux.  

Theory: When you experimented with as an auxillary default route for Linux, you provided a viable path from Linux to the network.  The problem was that Linux was fooled into thinking that packets could be delivered to <any> IP address via eth1, which is definitely not true.

Assuming you get this to work, you'll have to update your network routing configuration using the appropriate tool for your distribution of Linux.  

I may get flamed for this, but I favor putting this kind of stuff into a script that gets called from rc.local.   I usually do my upgrades via the fresh-install route,  so I depend on a backup copy of my script file to faithfully re-create my network environment.  I have upgraded many times, and everything worked as long as eth0 and eth1 were physically connected to the the right cables.   If nothing else, it makes me believe that I know how IP networks work.
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Expert Comment

ID: 2311469
Did it work?

Expert Comment

ID: 2315448
Have you enabled IP forwarding for the Token Ring card on the NT Server?  also,  Is your IP Masquerading setup aware that the 10.1.x.x hosts should be allowed to forward packets through the  


Author Comment

ID: 2317311
yes, I already had to default gw set to on the tr machines.

the command: route add -net netmask gw eth1
did the trick!  I believe the key was to tell it which interface to use (eth1 in this case) I had actually tried this same command before (minus the interface option) and it killed access to the internet.

Thanks for the tip and lesson!


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