'IPv6' Newbie with IPv6 address assigment

Cute Puppy asked:

I am new to IP v6 and I am looking to translate some existing private IPv4 addresses into v6 address assignment. Can someone please help me to answer/explain the questions below?

If I have an v4 address of:


What will the new v6 address to be?

I have been looking online @

or other sites,

Seems like they translated it directly to be:

  1. fe80::a0a:0 /118
  2. fe80::a0a:100 /118
  3. fe80::a0a:200 /118
  4. fe80::a0a:300 /118
  5. fe80::a0a:800 /118
  6. fe80::a14:100 /120

Can someone please explain to me how we get to /118 from either “/22 or /24” (1. and 5)

In addition,

I would like to create the new private address based on the Unique local address “fc00::/64”

How do I expand from there?

Does the following example look correct? => fc00::100 => fc00::200 => fc00::300 => fc00::400 => fc00::500 => fc00::600 => fc00::700 => fc00::800 => fc00::900 => fc00::a00 => fc00::b00 => fc00::c00 => fc00::d00 => fc00::e00 => fc00::f00 => fc00::1000 => fc00::4100

Any help is greatly appreciated it!!


My answer:

Unless you’re doing something highly unusual and bizarre, the smallest subnet you should use is /64. Anything smaller risks breaking various IPv6 necessities like neighbor discovery and the nice-to-have stateless autoconfiguration. Might even break DHCPv6, though I haven’t tried that myself.

To be crystal clear, the tool to which you linked appears to be generating bad data, and I wouldn’t use it. (Some of their other tools look fine, though.)

As for “translating” IPv4 to IPv6, you generally don’t. Instead, you run dual-stack, where each device talks both IPv4 and IPv6, with independent addresses for each protocol. The addresses themselves are provided by stateless autoconfiguration, DHCPv6, and/or privacy extensions, or (typically for servers) assigned manually.

So let’s say you get a block of addresses from your ISP, 2001:db8:1234:5600::/56. This gives you 256 subnets to work with, which is more than sufficient for a small office environment. If you need more than 256 subnets, you can get a /48 without too much difficulty, giving you 65536 subnets. That’s enough for all but the largest deployments.

If you can tell us more about what you’re actually trying to do, we may be able to provide better answers.

View the full question and any other answers on Server Fault.

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