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I have OpenVPN configured and have 5 dd-wrt router clients. I would like the machines on those routers to be-able to UDP Broadcast across all 5 networks.

I cannot bridge the interfaces(to my knowledge) because each router needs to be able to operate on its own should the VPN connection die (dhcp needs to work).

currently each router has its own /24 (eg 192.168.1.x) network. Is there a way to use IPTables to mangle the udp and forward them to all VPN Clients?

To summarize i need
1)to UDP broadcast to all routers and their clients
2)for all routers to be able to operate independently should the VPN go down

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As @James say, you will probably want to investigate using multicast. A normal IP broadcast does not cross a router and a VPN termination point is (usually) routed rather than bridged, for network efficiency reasons.

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I have been reading up about cisco's vpn solutions so this may be applicable to you but I can't guarantee it.

I would look at GRE Tunnels as they allow multicast to go over vpn's which is probably what you actually want. In the cisco world what you want is DVMRP, with Next Hop Resolution Protocol (NHRP).

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