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Re: [OpenStack][Neutron] Metadata over IPv6



On Wed, Mar 18, 2020 at 05:29:25PM +0100, Bence Romsics wrote:
> Hi Everyone,
> I'm also from OpenStack, just wanted to add an idea and a question.
> > > - 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?
> Alternatively we may delay this decision by adding a new data source
> 'OpenStackIPv6' and then the cloud image builder can order 'OpenStack'
> and 'OpenStackIPv6' in datasource_list as they see fit.

I'm not cloud-init expert but probably that is also good idea.

> My question relates to the use of link-local addresses as it is also
> commented on review.opendev.org. With my limited IPv6 experience, a
> URL with a link-local address but without a zone is incomplete, right?
> This is incomplete: http://[fe80::a9:fe:a9:fe]/. On the other hand
> this is complete: http://[fe80::a9:fe:a9:fe%25eth0]/. At the time of
> configuring cloud-init nobody will be able to predict the
> guest-internal interface names. Is it okay for cloud-init to take the
> incomplete address and discover the interface(s) to be used?

If I'm not mistaken, no matter which interface You will choose, metadata
received from Nova will be the same as it's metadata for the VM and Neutron just
needs to get VM's id and pass request to Nova API.
So in most cases it should probably works fine if cloud-init will try first
interface with IPv6 enabled.
But maybe config option to let this to be choosen by user would be good idea

> Thank you,
> Bence Romsics
> rubasov on freenode

Slawek Kaplonski
Senior software engineer
Red Hat