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I wonder how generally work the IP addresses on dedicated servers providers? The IP addresses are generally rented so you have no option to keep the IP's if you move to another provider? I see that many of those companies allow you to change some information in the IP WHOIS databases but that doesn't mean that you own the IP?

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If you're sticking with the same provider, in some cases they can reassign them to the new service, but there's no guarantees, and they may charge you some serious coin to make it happen.

If you're going with a new provider, you can't keep the IPs (unless they're assigned to you, which I'm going to go out on a limb and say they're not).

But it shouldn't be a problem. If you've done your network design right, renumbering isn't painful, it just takes a little bit of attention to detail. Of course, if your network design is a dog's breakfast, you're in for a world of pain, but you can use that as a learning experience for next time. Specific points to note include:

  • Keep a central IP address registry, like you would any other asset under your control.
  • Use DNS for everything.
  • Use service CNAMEs for everything you can.
  • Don't hardcode IP addresses anywhere you don't have to; anywhere you do have to (bloody firewalls), make a note in your IP address registry where it's hardcoded, why it was done, and link to documentation on how to change it.

Renumbering would be significantly easier, too, if some [expletive deleted][expletive deleted][expletive deleted][expletive deleted][expletive deleted][expletive deleted] caching DNS resolvers didn't override your DNS TTL values. Given that there is absolutely nothing you can do about it, you just need to have a plan to work around it.

First, do the right thing with DNS TTLs so that the well-behaved majority don't take a hit. Drop your TTLs to something nice and small (like 5 minutes) at least twice the current TTL before the cutover (why twice the current TTL? That way if you do it wrong, you can notice in time and fix it).

Make sure the contract on your old server overlaps your cutover date by at least a month. When you cutover to the new site, insert some NAT rules on your old server to redirect traffic to the new server. Only do this for selected ports (if you do the whole machine, you'll lock off your ability to get into it later, and you don't want to pay for all of the gibberish traffic -- portscans and the like -- that are the whitenoise of your traffic graphs). Keep an eye on your logs for connections from your old IP address on the new server -- when they've dropped to nothing, then the world has forgotten your old IP address, and you can drop the NAT rules on the old server and decommission it.

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IP addresses are NOT rented, they are assigned. In blocks of at least 4096 which are not splittable.

You want your own?

  • Become member of RIPE or your local registry (paying for it)
  • Get a block and an AS (Autonomous System).


Otherwise, sorry - the IP addreess is part of an AS assigned block, and at the end of the day this is not splittable.

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Ok so we are paying for example 10 dollars per month for each extra IP address to our dedicated server provider, isn't that a rent in the same way that they are renting us the dedicated servers? Anyway, thanks for the information because the rest of the comment has resolved me the question. Maybe what we can do is to keep one server or some other solution with them in order to point the IP addresses to our new location – Zillo Jul 16 '11 at 23:37
If your hosting provider presented the arrangement as "renting", then they lied to you. They can force you to renumber at any time, and you have zero recourse to keep your old numbers. – womble Jul 16 '11 at 23:45
The minimum block of IP addresses given out by RIRs varies per region. For example, AfriNIC's minimum allocation is a /24 (256 addresses). You'll also need to advertise the block given to you (BGP) through your upstream providers. And, depending on the policy of your RIR, sometimes it's possible to have an ISP sub allocate to you (i.e. RIR--(/12)->ISP--(/24)-->You) though, you don't have number portability if you need to move to a different ISP. Finally, get IPV6 addresses while you are at it. :) – Lmwangi Jul 17 '11 at 5:26
Nope, sorry, international routing is 4096 minimum block. Local registries can "subsplit" b ut that is not an AS in a fully independant form. – TomTom Jul 17 '11 at 6:22
You can not "keep a server and point ip addresses". IP adresses are handled like phone .- regional codes. When you move from a city to another your area prefix changes. Your old server ca nforward the traffic, but then you pay 2x the traffic on both ends (in and out, then in and out again). Just do what everyone else does, overlap times and change your dns. Not possible? Fire the person who hardcoded IP addresses instead of using dns. – TomTom Jul 17 '11 at 6:24

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