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Available IPv4 address blocks are exhausted and price per IPv4 address is increasing. However I read that 2/3 of IP address remains unused because they were assigned improperly at first stages.

Since looots of these assigned IP address are unused. Why organizations like IANA dont force its owners to give back unused IP address?

A lot of hosting providers are beggining to use NAT or IPv6 only for low end VPSs due to this fact.

I simply dont understand

NeDark
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  • RIPE and APNIC are already reclaiming unused IP blocks. ARIN won't be far behind. There are still plenty of IPs in Africa though, at least for a couple more years... – Michael Hampton Feb 02 '15 at 23:35
  • Those first allocations were done according to the design of IPv4. The real problem in how IPv4 addresses were allocated is not in those first assignments, rather it is in how the last half of the addresses were allocated. If the last half of the IPv4 addresses had been reserved exclusively for dual stack deployments, things could have looked a lot better today. Anybody returning IPv4 addresses now, are really just contributing to prolonging the problem. – kasperd Feb 03 '15 at 01:40

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Even if they could reclaim every unused IP (no easy task), it will only postpone things a short period of time. Delaying won't solve the problem.

Jim G.
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  • IPv6. It's the future! – Kate Feb 02 '15 at 23:48
  • @Kate Its been the future for what, 15 years now? – Grant Feb 03 '15 at 00:08
  • @grant hehe. Yup. – Kate Feb 03 '15 at 00:13
  • @Grant yes, the joke continues on RFC1606 :D http://www.ietf.org/rfc/rfc1606.txt – NeDark Feb 03 '15 at 00:45
  • @Grant That's what happens when you give people a 12 year deadline. They'll sit back and relax, and they will spend the first 13 years of the deadline that way. I recently did some calculations on the statistics published by Google. Those match up quite closely with a logistic growth curve which will reach 50% three years from now. A number which should have been reached 10 years ago (midway between December 1998 and February 2011). – kasperd Feb 03 '15 at 01:47
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You cannot just collect unused blocks and deal them out arbitrarily. Say, some site is allocated 120.0.0.0/8 and it turns out that half of it is not used, say, 120.128.0.0/9. There is a route to 120.0.0.0/8 announced through BGP. Now if you split the block, you need most likely two routes. Doesn't look exciting, but the routing tables in the Default-Free Zone (a.k.a. the Internet backbone) hold already way more than half a million entries. If you double a substantial number of routes, then the number of entries will grow considerably.

Now suppose the more likely case that the site has spread its addresses over the entire net block 120.0.0.0/8. Say, every other /16 is being populated, e.g. 120.1.0.0/16, 120.3.0.0/16, etc. If the site returns the unused "class B" blocks, and the responsible RIR deals them out to other sites, the number of routing table entries is increased by 255. If you do that for many sites, the number of routing table entries is going to explode, and this will be a serious bottleneck.

In practice the "average" scenario will probably be somewhere in the middle of the two scenarios, but as a matter of fact, there would be an awful lot of new "class C" networks that need separate routing table entries.

So why not simply renumbering networks and "defragmenting" the address space? Because renumbering means considerable downtime, since with IPv4 renumbering means in most cases to manually touch (or even reboot) each affected machine. And this is not taking into account all the hardcoded IP-addresses, which means you have to find an fix all affected applications. So from a practical point of view renumbering is next to impossible, and thus any plan to reclaim unused space will meet strong resistance.

countermode
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  • Often the most effective way to defragmentation is to move everything into a new piece of address space. And you would want to ensure that the new address space isn't completely crowded right as you move into it, so you want to ensure that the number of entries you move over, is only going to take up about half the space. This sort of approach to defragmentation would be extremely wasteful, if we were talking disk or memory, but it isn't a problem for IP addresses because adding a bit to the IP address doesn't mean that you have to double the amount of hardware. – kasperd Feb 28 '15 at 09:30
  • Bottom line is - defragmentation works great in an IP address space, which isn't too crowded. IPv4 is way more crowded than it was ever intended to be. It is way too crowded for defragmentation to be feasible anymore. Research has shown, that the point where an address space becomes too crowded to be easily managable is when around 80% - 90% of the **bits** in the addresses are used. So IPv4 shouldn't be used with more nodes than can be addressed with about 27 bits. – kasperd Feb 28 '15 at 09:34
  • And this is one reason why ISPs are encouraged to give out large IPv6 subnets, ideally much more than the customer will ever possibly need. (RFC 6177) – Michael Hampton Mar 01 '15 at 17:20