LANCOM Support Knowledgebase Document No. 1811.1412.0723.RHOO - V1.00

Connecting LANs with the same IP address ranges across a VPN (N:N mapping)



Description:

An N:N mapping is used to connect networks with the same IP address ranges. This translates several IP addresses ("N") from the local network explicitly into several ("N") IP addresses of any other network. This translation prevents an IP address conflict.

The rules for address translation are defined in a static table in the LANCOM router. This involves specifying new IP addresses for individual LAN devices, for subnets or for the whole LAN, which are then used by the devices to communicate with other networks.

Address translation is performed "outbound", i.e. only outgoing connections from the LANCOM device are subject to address translation. Once a connection has been established, data exchange is of course possible in both directions.

"Inbound" address translation for arbitrary incoming connections is not supported. Instead, outbound address translation must be set up on the corresponding remote device.

The following example shows how the network configuration below (both LANS are C-class networks) can be connected via a LANCOM dynamic VPN:






The N:N mapping translates all addresses within the LAN into a new range of addresses for communication with the remote network.

Company A's network is translated, for example, to the range 192.168.200.x, while company B's network is translated to 192.168.150.x. Each LAN is now accessible by the other at these new addresses.
The device being addressed is not located in the local network, so the request is forwarded to the gateway and routed to the remote network, as desired.


Procedure:


Step 1 - set up VPN connections:

The VPN connection must first be defined, with the destination network of 192.168.150.x being specified in one router and 192.168.200.x as destination network in the other router.

Step 2 - configure N:N mapping:

The N:N table can be found in LANconfig under: Configure: IP router -> N:N mapping -> N:N-NAT table

Router with destination network 192.168.150.x:



Router with destination network 192,168,200.x:



The original source IP address is always 192.168.100.x, which is mapped to a different network at each end of the connection.

Catchwords: mapping; n:n
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