This is my complicated and long question. First let's talk about the context.
Network topology: (RT stands for router)
PC A --- RT A --- RT C --- RT B --- PC B
(RT C has a WAN NIC connected to "the cloud")
With this situation :
- PC A must send a packet to PC B
- Default routes direct packets to the cloud
- We haven't access to RT C's configuration
- RT C only knows how to join network A, not network B
- RT A knows about network B
- RT B knows about network A
RT C's routing table:
Destination NIC Gateway 0.0.0.0 WAN Cloud Network A LAN A RT A's WAN
RT A's routing table:
Destination NIC Gateway 0.0.0.0 WAN LAN A Network B WAN LAN A
RT B's routing table:
Destination NIC Gateway 0.0.0.0 WAN LAN B Network A WAN LAN B
I would like to permit PC A and PC B to communicate, but I don't have access to RT C. Networks B and BC are new.
Can PC A send a packet to RT B's WAN NIC (which is possible) and "ask RT B to direct the packet to PC B" ?
I believe replacing RT B with a VPN server should do the trick, but I would like to know if it is possible to make it without establishing a new connection.