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I have a /29 network of publicly-routable IPv4 addresses from my ISP. I would like to migrate to /28 network of publicly-routable addresses. Unfortunately, my ISP can not extend the current /29 network, but they gave me a new one. This means that for a next month, during the migration period, I can use both the old /29 network and new /28 network. All the web-servers have DNS A-records. What are the techniques/options to gracefully migrate web-servers from old /29 network to this new /28 network? I mean it's easy to change the network configuration in servers and restart the services, but how to ensure that web-pages are available to viewers? I guess one option would be to configure round-robin DNS in a way that domain-name resolves either to IP address in existing /29 network or to new one in /28 network and for few days, HTTP server listening on new address, just redirects to old IP address. After few days(or as long as it takes DNS records to populate across the DNS system) I would remove the old IP from DNS configuration. Will this work? Or are there better practices?

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Very simple.

  • Make sure server listens to both addresses.
  • Switch DNS.
  • Wait 2-3 times zone validity (to be safe)
  • Disable / remove old addresses.

Finished.

No need for round robin etc. - users will gradually start using the new IP addresses as the DNS entries switch over.

This is also the (only sensible, in most cases) way to handle this when you switch datacenters - run both in parallel and migrate slowly.

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