IP addressing

I need to setup a company network and looking for feedback.

We have following 6 locations
1) NYC = 2000 machines
2) NJ = 500 machines
3) London = 600 machines
4) Brussels = 200 machines
5) Hong Kong = 100 machines
6) China = 400 machines

Which class IP address I need? I believe I can not use C class because I have more then 254 nodes. These all machines should be interconnected so they can send mail from outlook and also able to browse internet

Additionally, is there a way to use private IP address and connect all sites together?

Thank you

Classes are kinda irrelevant with VLSM. I would pick private subnets for each site which account for all the machines and then some. You can use private addressing and setup tunneling between sites, or setup a L2/L3 VPN with your provider, though you may need two WAN links per site to do that - or just use one site as the gateway, but that would be bad given they are international links.

I would go along with that. Maybe setup Branch Office VPN connections to a central site and control all internet traffic through the single point, this way you can setup your security policies and enforce them for all sites.

This would all depend on the size of the links that each site would have and also the size of the link at the main site.

Just make sure that each site has different NetworkID's that do not overlap with any other site otherwise when you come to interconnect them you will have serious issues (although you can get around it by setting up NAT'd VPN's but it really isn't pretty and i would never plan to go do that route, this is really only if you have mergers and the two companies are on same ip ranges).