I have 1 internal and 1 external DNS server. I will migrate a set of existing external IP addresses to a new set of external IP addresses. The old IP addresses will be disabled on a specific cut off date. What is the recommended approach on DNS records for the IP migration? Do we need a new DNS server to cater for the migration to the new sets of IP? Can we use the existing DNS server, append the new IP addresses prior to the cut off date while keeping the old IP addresses? Will the new IP take effect automatically on the cut off date or is there any action to be carried out at the DNS server on the cut off date?