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routing with two identical subnets

Posted on 2004-03-23
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Last Modified: 2012-06-27
Hi,

I have two locations with a identical ip ranges / subnet and want to add a new pc to this subnet on both locations as beeing a part of the LAN. I expect problems when "simpley" connecting to the router because it will have two destinations. So in brief i want to connect 2 pc's to 2 locations with identical subnets where the router acts a a direct "cable" connection from pc 1 to location 1 and pc 2 to location 2.

Is it possible to configure a CISCO 2611XM with a NM-4E card in such way? Changing the ip addresses is not an option since it is a 24 hour gas production environment.

roger.vander.werf@"n.o.s.p.a.m."nl.yokogawa.com
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Question by:rogervdwerf
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4 Comments
 
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Expert Comment

by:pseudocyber
ID: 10657022
The only thing I can think of is bridging the two networks instead of routing them.

Even if you did a one to one NAT, you'd still have a problem sending to the worksationA or B because the network wouldn't know to send it to the router because before it put in the router's Ethernet address it would do a binary add to determine if it was local or not, see that it is (based on it's IP address and local subnet mask) and then send it via Ethernet at layer 2 to the local machine, not to the remote machine via the router.

If you want to connect two IP networks, you REALLY, REALLY need to make sure they're not the same network, unless you intend to bridge them.
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Expert Comment

by:dndgi
ID: 10659419
If you have a second router, you could do what it is I believe you are asking.

The problem lies in 'connecting' both networks to the same router.
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lrmoore earned 125 total points
ID: 10660575
How are you physically connecting these two locations?
Assuming a router at each end, and either a WAN or LAN connection between them, you simply bridge the two interfaces at each end (Wan interface and local LAN interface).
However, you cannot have any two systems with the same IP address, on either side. EVERY sytem must have a unique address, but they can all be in the same subnet.

On a 2600, the commands would look like:

bridge 1 protocol ieee
!
Interface Fast 0/0
 description Local LAN site A
 no ip address
 bridge-group 1
!
Interface serial 0/0
 description WAN link to site B
 no ip address
 bridge-group 1
!




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Expert Comment

by:msprinkle
ID: 10678723
Install nat devices in front of each subnet and nat everthing outbound to the router.  
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