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Re: [OpenStack][Neutron] Metadata over IPv6



> On 11 Mar 2020, at 20:13, Ryan Harper <ryan.harper@xxxxxxxxxxxxx> wrote:
> On Wed, Mar 11, 2020 at 4:39 AM Slawek Kaplonski <skaplons@xxxxxxxxxx> wrote:
> Hi,
> Hi Slawek,
> Thanks for reaching out to the cloud-init community.
> I’m OpenStack Neutron developer. Since some time we have proposed spec [1] about Metadata over IPv6 in IPv6 only networks.
> This spec proposes to use fe80::a9fe:a9fe IP address as it is equivalent of in IPv6 link-local subnet.
> According to [2] I know already that cloud-init can be configured to use any metadata urls with “metadata_urls” so we can use such IPv6 address (or any other) and can be configured to be used in cloud-init on guest vms.
> But as cloud-init is one of the biggest users of Metadata service, I would like to ask cloud-init community what do You think about it and if this will work for You. 
> Any feedback here or in the spec's review will be appreciated :)
> Some initial thoughts and questions:
> - In what order should cloud-init try ipv6 and ipv4?
>    - cloud-init would prefer to know which one it should use so we don't timeout on an endpoint that isn't there.

I would say that it it could be checked what IP addresses are configured in the guest OS already and use correct one if only one type of addresses is there. If there would be both IPv4 and IPv6, it could try IPv4 first as it is like that now. What do You think about such solution?

>    -
> - cloud-init's EphemeralDHCP code currently relies upon dhclient and ipv4 ips/routes; this will need updating to work with v6; what is needed use fe80::a9fe:a9fe ?

As this is link local IP address it should be reachable without any configuration if IPv6 is enabled on the interface in the guest.

> - is there a chance that Metadata is available over either v4 or v6?
>    - would the data ever diverge?

I don’t know if this data can diverge in the future.

> Thanks,
> Ryan Harper

Slawek Kaplonski
Senior software engineer
Red Hat

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