@irtaza9 OK so you have VLANs per DC. That means VLAN5 in KPK-DC1 and VLAN5 in RWP-DC4 are unrelated and machines in those VLANs cannot communicate directly without going trough some router? This goes back to my original answer. You have to take into account network connectivity when deciding what DC/pool to select for VM provisioning. If you have a few VMs in VLAN5 in KPK-DC1 and you decide to provision some more VMs at latter time that require direct connectivity with existing VMs, you have no choice but to provision them in VLAN5 in KPK-DC1.
Regarding VLANs in general, this is all fine except you can scale it up to a few thousand of VLANs per DC so it will impose a hard limit on the number of isolated network segments (i.e. users/customers). Some weapon of choice among most cloud providers is to use some kind of network overlay like VX-LANs, GRE tunnels and such but this has issues of it's own. For a start, these kinds of networks are software defined in nature (SDN), require an orchestrator and network nodes that run in software. You can leverage some hardware acceleration here and there but it will still be software oriented and have scaling and latency issues. There is no silver bullet and most providers hide their network implementation details.
All in all, a good, scalable and fast networking i probably the toughest thing to implement in any large scale cloud provider... and I'm definitely not a network engineer so I can't say much about it .
