The first site (main site) is already using an RVS4000 and doesn't need any change.
The second site (remote site) already has modem/router installed. This modem/router will not support many changes, as it has a built-in voip pbx and phones are directly connected with this device. So this one will still need to act as a router.
My first idea is to
1/ connect the WAN port of the RVS4000 to a LAN port on the modem/router, and connect a new switch to a LAN port on the RVS4000. Computers will be connected to this new switch.
2/ the old switch will still be connected to a LAN port on the modem/router, and serve IP phones only
So basically PCs will be connected to the main site through the VPN tunnel.
It means that we'll have 2 subnets : 1 for the phones (dhcp on the modem/router) and 1 for the PCs (dhcp on the rvs4000).
This is quite OK, but it also means that, in order to forward traffic from the outside to any LAN PC, I'll have to forward twice the traffic (first on the modem/router to the RVS4000, then from the RVS4000 to the PC).
Is there any better way to add the tunnel to the existing network? Ideally, I'd like to squeeze the RVS4000 somewhere on the network, and make it take care of the VPN only... and not have to change anything on the existing subnet config.
I've also seen some words about the gateway/router mode, but the documentation I've found is not really helpful. I've quite understood that, when the RVS4000 is behind a router, it should be setup in router mode, but I don't really understand how better it is.
Also, in all cases, all the usual internet traffic on the remote site should be routed through the modem/router, not through the VPN.
It sounds like you have no other choice but to connect the RVS4000 behind the modem/router. In that case you will have to try to forward ports or create a DMZ in the modem/router to allow VPN traffic to the RVS4000. This is not ideal but may work. In router mode you cannot use the RVS4000 as a VPN server.
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