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New Member

Single IP subnet in two physical locations

Is it possible to create a single IP subnet in two physical locations over a WAN link, so that the link is transparent to two hosts, one in each location, for the purposes of network browsing etc?

I thought that perhaps DLSW+ might do this, with no ip address and a bridge-group on the LAN interfaces, and dlsw bridge-group globally, but I feel that this somehow isn't what DLSW+ is intended to do.

Can anyone help?


Re: Single IP subnet in two physical locations

You can have the same IP network at each location, provided the equipment which connects between the two sites act as a bridge. If its two routers you are using, configure all their interfaces (serial and ethernet) to fall in the same bridge-group. There is no need for DLSW, as long as you are using protocols such as IP, IPX etc. DLSW is used to transport protocols such as SNA or netbios over IP.

Cisco Employee

Re: Single IP subnet in two physical locations


Re: Single IP subnet in two physical locations

As a more complex solution, but one that will provide some additional options, consider doing a dual NAT.

Depending on the network size on either end of your WAN, bridging will probably work, but the traffic flows for anything other than a small network can congest your WAN link.

By using dual NAT, you gain the advantages of traffic management and filtering, reduce the broadcast domain to a manageable level, and would be more manageable overall for address assignments, expansion, virus/worm control, and other issues that don't come to mind until it's too late.

If Dual NAT seems too complicated, consider using VLANs with a trunk through the WAN. You'd be able to do some traffic control by VLAN assignment, put machines that need to be in the same broadcast domain on the same VLAN, and set up a higher priority on a management VLAN so if something "went wrong" on the other side, you can still get through the WAN to handle it.

For anything other than a fairly small network, bridging can get messy pretty quick, especially with a Microsoft-based network (lots of broadcasts if not done properly).



New Member

Re: Single IP subnet in two physical locations

can you expand on this dual nat?

I am very interested in how i may be able to use this to my advantage for a HA/DR solution on our corporate network