Generally, one subnet cannot communicate with another subnet without having a router in between. An unmanaged network switch, for instance, cannot route packets between subnets. Whatever port is established as the uplink controls the subnet for the switch. The router, however, is designed to allow one subnet to communicate with the other through the use of a route. Often, if there is a perimeter router in the picture, then a firewall may also block the traffic, but most firewalls are configured to allow traffic outbound (particularly on port 80/443) so that the connection to the ROV should work, but not the reverse. Note that the connection is bidirectional, but it needs to be started from the “internal” or “protected” side of the firewall.
Your home computer can get to other subnets on the internet because your gateway device has routing capability (and almost certainly uses Network Address Translation (NAT) which is impossible without routing capability).
The VPN shouldn’t really factor in to your issue in my thinking because VPNs are encrypted point to point tunnels where all traffic to the destination network is effectively ignored by any network equipment in between. There is no routing involved with the VPN, though, so different subnets still won’t talk without being routed at one or the other ends.
One thing to note is that you can check for connectivity using ping. If you can’t ping the ROV, then it’s unlikely that you’ll be able to connect to it.
ping 172.70.1.xxx
To test the port, you can use a telnet client or ftp. For telnet, you would do this:
telnet 172.70.1.xxx
If the screen clears and goes black then you have a connection. In fact, iof you know the protocol, you could type in commands.
For instance:
telnet www.subsearovers.com 80
[the screen will turn black]
type:
GET / HTTP/1.1
[hit enter twice]
That’s for HTTP protocol, which is what our ROV uses. The point being that you can check a host using ping and check a service on a port using telnet. If you don’t have a telnet client, you can use an FTP client, but all you’ll be able to establish is a connection. You’d be looking for the message “Connected to www.subsearovers.com”
A network diagram would be helpful
