Virtual Networks have default connectivity, but are totally isolated.
VNet peering
VNET A can talk to VNET B via a private IP address with a fast and low-latency connectivity.
Peering supports cross-subscription connectivity and supports cross-region connectivity.
But, limitations :
we cannot have address spaces that overlap (for example, VNAT A and VNET B have the same address space and so, the peering will not work)
we cannot have transitive routing (VNET A cannot talk to a VNET through VNET B).
