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My company has a local network with hosts on public IP range 199.5.x.x obtained from our ISP and a subnet of 255.255.255.0. We do not use DHCP. When the number of users have increased and we are running out of IPs, we would like to upgrade our network from class C to class B to accommodate more hosts. Is there any way I can do this through the use of subnets without involving the ISP?

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You need all your hosts to be on public IPs? (all you hosts are public servers?) –  laurent Oct 30 '12 at 14:48

3 Answers 3

You cannot magically create new IP addresses.

Instead, you need to use a router with NAT to put multiple computers behind a single public IP address.

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You can not upgrade from class C to class B. These classes of subnets are no longer in use. Instead Classless Inter-Domain Routing (CIDR) is used these days.

You will either have to:

  • Contact your ISP, ask for more IPs. Explain to the ISP why you need them.
  • Or use less IPv4 IPs (can you use IPv6?)
  • Or use a ugly hack called NAT. It is an abomination to the way TCP/IP works and it may require a lot of workarounds to get back to full functionality. (E.g. old fashioned TCP and NAT is fun).
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You really should use DHCP to handle the IP addresses in your intranet. You can set this feature up on your router. It is easy to do and it will automatically take care of all of your IP address needs for you.

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