ISP has given new public ip pool so how i can configure and do the natting with private ips, existing ip pool is working fine.
It's difficult to tell you what exactly to do when I'm not sure where you're starting from.
Describe your current and desired state in more detail (you can use "fake" IP addresses, if that helps).
A network diagram would likely be very helpful.
As long as the ISP is routing the new IP pool to your gateway you can start using the new IP's from the pool for NAT directly, just add 1 of them to a server you want to use the new IP on and test.
Keep in mind that you can use all addresses including the network and broadcast addresses.
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