Connect two locations with same subnet

Hello,

I have to move part of my servers to another physical location (need
more space).

Actually the situation is:

[internet]
|
[our ISP]
| (here there is a dedicated physical fiber connection)
[router]
|
[switch]
|
[servers]

We move our router directly to our ISP, so the situation will be:

[internet]
|
[our ISP]
|
[router]
|
[switch]
| (now the physical fiber connection is here)
[switch]
|
[servers]

No trouble here. We have to do this move because our ISP does not have
enough physical space in his server farm to store our server (we talk
about 100 servers). But the ISP has a second server farm (B) that can be
connected with the first one (A), (C) is our server farm in this moment.
So the final situation will be:

[internet]
|
[our ISP]
|
[router]
|
[switch(A)]---[switch(B)]-[servers]
|
| (the physical fiber connection is here)
|
[switch(C)]
|
[servers]

Now the trouble is that our ISP cannot connect with a dedicated
connection for us A and B, but he can connect with two modems. I'm not a
newtork expert, but our ISP told us that we need a VPN to connect A and
B. Our goal is to "transparently" move servers from C to B without
changing IP or routing, as if the two networks are connected to the same
switch. All our servers have a public IP address in the same subnet
(x.x.x.x/24), servers in C has to "talk" with servers in B (and
viceversa of course) without troubles and C and B have to access (and be
accessible in) internet via router in A. There is a way to connect in a
transparent way all the 3 physical separated network? Thanks in advance.

Nuke wrote:

> Now the trouble is that our ISP cannot connect with a dedicated
> connection for us A and B, but he can connect with two modems.

Errata: A and B connected with two routers.