Applications that break when not using /64

Jeroen Massar jeroen at
Tue Jun 17 21:13:12 UTC 2014

On 2014-06-17 22:36, Grzegorz Janoszka wrote:
> On 2014-06-17 22:13, David Conrad wrote:
>> On Jun 17, 2014, at 12:55 PM, Grzegorz Janoszka <Grzegorz at>
>> wrote:
>>> There are still applications that break with subnet smaller than /64,
>>> so all VPS providers probably have to use /64 addressing.
>> Wouldn't that argue for /64s?
> /64 netmask, but not /64 for a customer. There are application which
> break if provided with /80 or /120, but I am not aware of an application
> requesting /64 for itself.

Except for SLAAC that requires a /64 due to it using EUI-48 to make up
the address, which "applications" are these, as those applications are
broken by design.

An application (unless it is a protocol like SLAAC or something else
similarly low-level) does not need to know about prefix sizes nor
routing tables.

Thus, can you please identify these applications so that we can hammer
on the developers of those applications and fix that problem?

>>> /64 for one customer seems to be too much,
>> In what way? What are you trying to protect against? It can't be
>> address exhaustion (there are 2,305,843,009,213,693,952 possible /64s
>> in the currently used format specifier. If there are 1,000,000,000
>> customer assignments every day of the year, the current format
>> specifier will last over 6 million years).
> Too much hassle, like too big config of your router. If you have 1000
> customers in a subnet, you would have to have 1000 separate gateway IP's
> on your router interface plus 1000 local /64 routes.

Wow, you really stuff all the customers in the same VLAN and thus the
same routed IP.... lots of fun those other customers will have with
that, especially as a lot of folks simply do not know that IPv6 is
already there and has been enabled in their distribution, applications
and kernels for many many years...

As for "why" VPSs are doing the limited number of IPs per VM, simply:

And if you want more, you can buy more... hence if you want more, vote
with your money and take your business elsewhere...


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