[ipv6-wg] [atlas] What to do with RIPE Atlas probes that have only a ULA as IPv6 address?

On 26/03/2015 08:26, Benedikt Stockebrand wrote:
> Jen Linkova <furry13 at gmail.com> writes:
>> But wait, if a probe has RFC1918 addresses only you do not mark it as
>> 'no v4 connectivity', right?
>> If a probe has a address of a global scope (v4 or v6) but could not
>> reach the outside world it means the connectivity is broken. So IMHO
>> it makes slightly more sense to mark ULA-only probes as having broken
>> connectivity.
> 
> just wondering: If I use RFC1918 addresses with IPv4 I might still have
> Internet access through a NAT gateway.  If I have only ULA, then I may
> reasonably expect there's no NAT, so there's a fundamental difference
> here.

It's quite valid for a device to have a global address but not be
connected to the internet; a network might need to be globally unique
even if it's not globally reachable. It's rare in v4, and pretty rude in
a time of scarcity, but it's technically valid.

The question of whether a device is configured to be connected to the
internet isn't answered by the scope of the address, but by the presence
or absence of a default route.

If a probe has ULA but no default route, that sounds to me like an
entirely correct configuration. The behaviour Philip observes, where the
system call fails immediately, is the desirable behaviour (and would
cause a higher level application to fail over to IPv4.)

So I think that the proposal is right to consider such a device "not
connected to the IPv6 internet" as opposed to "improperly configured."

(But I want to hedge on one thing: I'd like to still see the reason for
the "not connected" decision recorded - i.e. no address vs. ULA but no
default - so that we can see trends over time.)

All the best,
Dave

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