Overlapping Network

[rouven.heim]

I´ve the situation of 2 overlapping networks.

The provider has installed a 3rd Party Router and gave us the 10.10.194.0/30 network. The concept is that the the 3rd Party Router is not directly connected to the LAN but throug a second router(e.g. Cisco) to the LAN.

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WAN---(3rdPartyRouter)---------------------(CiscoRouter)----------------(Switch/LAN)

.........................................|.............................|.......................|

......................... 10.10.194.1/28....10.10.194.2/28...10.10.194.17/24

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At the position of the CiscoRouter was before an AS/400 System. With the AS/400 this was possible, also with a 3COM Router this would work. What can I do with the Cisco Router?

Thanks,

Rouven

[rsissons]

I am not sure that I fully understand your topology here but if you require the same network on multiple interfaces on the same router then the easiest way would be to turn off ip routing and just bridge the traffic.

If you need to route the traffic on some interfaces, then you need to configure IRB, Integrated Bridging and Routing. See the following URL for some examples -

http://www.cisco.com/univercd/cc/td/doc/product/l3sw/8540/rel_12_0/w5_13/config/6cfg8500.htm

[rouven.heim]

I try to explain it better!

The Router from the ISP has an Interface configured with the ip address 10.10.194.1/28. This interface is connected to an Cisco Router Interface which has the ip address 10.10.194.2/28. The second interface of the Cisco Router has the ip address 10.10.194.17/24 and a third interface has the ip address 10.10.191.1. Now, when i try to enable the first and the second Interface of the cisco router the first comes up but the second won´t , because of a overlaping configuration.

Message:

% 10.10.194.0 overlaps with FastEthernet0/0

FastEthernet0/1: incorrect IP address assignment

The RFC950 says this should work and Cisco says i would support this rfc. With a 3COM Netbuilder II or an NT Machine ( using as a router) this is not a problem but with Cisco.

Is there a way to get this running? I use Cisco 2611XM with 1 NM-1E Interface and IOS IP Only v12.2(8)T1.

I know this is not a good configuration, normaly i would use a seperate Subnet for the connection between the ISP Router and the Cisco Router but this i the way the ISP connects the locations. Before the cisco there was a AS/400 machine with 3 interfaces and the same configuration. Now its time to replace the AS/400 with a cisco router!

Thanks,

Rouven

[ruwhite]

You can't overlap addresses between interfaces.... Does RFC950 really say you should be able to?

:-)

Russ