When you run out of RFC 1918 IP address space to allocate, what's best to assign?

Once you've used up all your private RFC 1918 space, are there certain non RFC 1918 IP blocks that are best practice to use for internal addressing?
amigan_99Network EngineerAsked:
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Paul MacDonaldDirector, Information SystemsCommented:
What you do on your private network is up to you as long as you keep it private.  It seems highly unlikely you've used up all the IP addresses in any of the available private networks, given that the smallest one allows for 65,000 addresses on one network.

What address range are you using now, and what subnet mask?
amigan_99Network EngineerAuthor Commented:
Large swaths of address space were assigned for AWS environments and there have been mergers that have brought still more wide swaths. I can probably find space of I dig. But I wondered theoretically if you wanted to or needed to - is there an address space that's not in the RFC 1918 range but in reality not used?
17+ million hosts? I guess this is a theoretical question anyway but the answer is, at this point, to switch to IPv6 addressing. In IPv6 which is a 128 bit address, as opposed to the 32 bits of IPv4, there is the potential of trillions or greater private IP addresses.
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nociSoftware EngineerCommented:
What are you running that consumes > (65536 * (1 + 16 + 256) ) -  6 = 17.891.322  addresses?
(if all 1918 space is confiugured as 3 separate networks)....
17+ million systems???

Well then you OBVIOUSLY need ipv6....  The least you get is 1 * (2^64) addresses
amigan_99Network EngineerAuthor Commented:
We have a dev team that likes to have a ginormous amount of room for growth in each of the subnets they assign to their various environments.
Paul MacDonaldDirector, Information SystemsCommented:
You're not answering the questions we're asking, and we can't provide an answer unless you do.  We're incredulous there's no address space left - it's MUCH more likely it's being mis-managed.

But to answer your core question: No, there's no super-secret address space only certain sysadmins know about that anyone can use on their private network.  But as I noted before, what you do on your private network remains private as long as you keep it private.

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With IPv6 there is a total universe of ~340,000,000,000,000,000,000,000,000,000,000,000,000 possible addresses or 2 to 128th power. The Internet Assigned Numbers Authority (IANA) (sounds like something out of Hitchhiker's Guide) has only released a small percentage of the entire pool. Frankly, I'm still getting my head around IPv6 but based upon the size of the pool it's probably that there will never be a need for private ranges except in translating IPv4 to IPv6 addresses. Undecillion is so big a number that it's hard to even grasp to some degree.

Anyway, that's my take on it!
David FavorLinux/LXD/WordPress/Hosting SavantCommented:
Follow Matty's + noci's suggestion.

If you dev team is assigning massive private network spaces, the likely fix is for them to change their procedures, as it's unlikely you'e used up even a fraction of 17 Million IPV4 addresses.

If you can't do this, you must switch to IPV6, where you'll have the same exact problem if your dev team's procedures continue with this type of broken thinking.
amigan_99Network EngineerAuthor Commented:
Thanks much. Yes, it's been mis-managed with 10.*/16 spaces handed out like candy at Halloween.
nociSoftware EngineerCommented:
There is one cure against address mis-management: replace address management. Revoke all and redesign...., probably in another order.

Or start a new account and do the same there. (the environments will be separated and stay separated).
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