I have a situation of a main office and branch office with 2820 routers at each end. The main office LAN is 192.168.3.0 / 24 and the branch office LAN is 192.168.2.0 / 24. At the main office there is VOIP and it's network is 192.168.4.0 / 24. I would like to create a VPN to allow VOIP traffic to go to the branch office where there there are only a few phones and it would be sensible to incorporate them into the main office infrastructure and save cash, if possible. I do not need to provide access to shared folders, printers etc. between the main and branch offices.

Is it possible to do what I want with the 2820s? I've been investigating and don't think I can do it because the 2820 at the main office would have the 192.168.3.0 and 192.168.4.0 (presumably separate VLANs) connected and the branch office would have the 192.168.2.0 and another local network (maybe 192.168.5.0 / 24) for the phones, again on separate VLANs.

If it's not possible, what would be the most cost-effective (and easily configured/managed) way of doing this?

Thanks for your time (and patience!).

How do you have two subnets set up on the 2820? It only supports one subnet really so any way of adding the 192.168.4.0 subnet would be awkward or does that voip subnet use another router on that site?

Thank you for your response.

The VOIP 192.168.4.0 network doesn't touch the Draytek and the phone system at the branch office is a handful of phones which, again, don't touch the remote Draytek. I don't know if it's relevant, but the VOIP phones are all connected to POE switches. The current setup is:

Main Office:
192.168.3.0 / 24 LAN <--> Draytek 2820 <--> Internet
192.168.4.0 / 24 VOIP network interconnected via POE HP switches

Branch Office:
192.168.2.0 / 24 LAN <--> Draytek 2820 <--> Internet

What I'd like to do is create a VLAN on the router at each end, connect the 192.168.4.0 / 24 VOIP network at the Main Office end and mirror it at the Branch Office (probably a 192.168.5.0 / 24) then have a VPN to take traffic between the VOIP VLANs from Main <--> Branch.

I don't think this can be done with the 2820s but would welcome any easy workaround. Alternatively, we might be able to upgrade the routers at both ends if one the models could direct the VOIP VLAN into a VPN tunnel connecting them. If this is the only solution, what would be an appropriate model?