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Re: [OT] IP address collisions




Dan Purgert <dan@xxxxxxxx> writes:

> Nicholas Geovanis wrote:
>> On Thu, Apr 18, 2019 at 7:57 AM Michael Stone <mstone@xxxxxxxxxx> wrote:
>>
>>>
>>> No, the ULA is the IPv6 equivalent of RFC1918 space--you can use it
>>> internally without central registration by choosing a subnet from
>>> fd00::/8. The space is so much larger that it's much less likely that
>>> two sites would pick the same prefix, but there are no guarantees.
>>>
>> But isn't it irrelevant whether they pick the same prefix or not? Routers
>> that respect ULA and RFC1918 shouldn't route any traffic destined to them
>> off the logical subnet. Right?
>
> No.  RFC1918 / ULA are merely "unroutable on The Internet" (as in, they
> cannot be directly accessed from the public internet).  You can freely
> route between them on "private" networks to your heart's content.
>
> For example, I have the RFC1918 subnets
>
>  - 192.168.1.0/24, .2.0/24, .10.0/24, and .20.0/24  (LAN networks)
>  - 10.90.0.0/16 (VPN[1])
>
> [1] way overkill, but lets me move around a bit in case a hotel is using
> part of that range. (I only have the server hand out a /24 out of that
> range, but the LAN's routing table uses the full /16).

I use 192.168.13/24 for my home machines, externally available on my
VPN as 10.13.13/24, on the theory that hotels will be sensitive to
offending superstitious guests.  Haven't had a problem yet!