using "reserved" IPv6 space

Seth Mattinen sethm at
Tue Jul 17 22:21:22 UTC 2012

On 7/13/12 7:38 AM, -Hammer- wrote:
> OK. I'm pretty sure I'm gonna get some flak for this but I'll share this
> question and it's background anyway. Please be gentle.
> In the past, with IPv4, we have used reserved or "non-routable" space
> Internally in production for segments that won't be seen anywhere else.
> Examples? A sync VLAN for some FWs to share state. An IBGP link between
> routers that will never be seen or advertised. In those cases, we have
> often used It's reserved and never used and even if it did
> get used one day we aren't "routing" it internally. It's just on
> segments where we need some L3 that will never be seen.
> On to IPv6
> I was considering taking the same approach. Maybe using 0100::/8 or
> 1000::/4 or A000::/3 as a space for this.
> Other than the usual "Hey, you shouldn't do that" can anyone give me
> some IPv6 specific reasons that I may not be forecasting that would make
> it worse doing this than in an IPv4 scenario. I know, not apples to
> apples but for this question they are close enough. Unless there is
> something IPv6 specific that is influencing this....

Don't, because there's already a /10 defined for such things. It's
called ULA (unique local address) aka RFC 4193. ULAs are not globally

Here's a calculator that will generate a random one for you:


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