[v6ops] Re: DHCPv6 PD in a multi-prefix environment

[David Farmer <[e-mail]>]

On Thu, Jul 25, 2024 at 11:16 AM Timothy Winters <[e-mail]> wrote:

> Hi David,
> On Wed, Jul 24, 2024 at 9:38 AM David Farmer <[e-mail]> wrote:
>
>> On Wed, Jul 24, 2024 at 10:23 AM Timothy Winters <[e-mail]> wrote:
>>
>>> Hi Ole,
>>>
>>> I think we could add a Section to the draft for ULAs in particular.   If
>>> you have ULAs enabled on the Customer Edge Router, delegating makes sense.
>>>   It's a use case that I didn't include, but I can't think of a good reason
>>> not too.
>>>
>>> David,
>>>    The draft doesn't exclude ULAs it's just only applied to prefixes
>>> delegated on the WAN.
>>>
>>
>> Ok, now I need clarification.
>>
>> LPD-2 concerns the prefixes assigned to the CE router's local interfaces.
>> Do you expect LPD-2 to override RFC7084: L-2?
>>
> No
>
>> Does that mean that if you implement CPE-lan-pd, you no longer have ULA
>> on even the CE router's local interfaces?
>>
> No, I was poorly trying to communicate that the ULA prefixes aren't
> delegated beyond the LAN interface unless they were provisioned on the WAN
> interface.
>
>>
>> LPD-2:
>> The IPv6 CE Router MUST assign a prefix from the delegated prefix to each
>> of its LAN links. If not enough addresses are available the IPv6 CE Router
>> SHOULD log a system management error.
>>
>>
>> RFC7084: L-2:
>> The IPv6 CE router MUST assign a separate /64 from its delegated
>> prefix(es) (and ULA prefix if configured to provide ULA addressing) for
>> each of its LAN interfaces.
>>
>>
>> It is LPD-4 that speaks to what prefixes are advertised to DHCPv6-PD
>> Clients.
>>
>> LPD-4:
>> After LAN link prefix assignment, the IPv6 CE Router MUST make the
>> remaining IPv6 prefixes available to other routers via Prefix Delegation.
>>
>>
>> So, at the very least, we want a CE Router capable of PD distribution to
>> generate a ULA prefix and assign subnets to each local interface, as
>> RFC7084 does now. I'm with Ole, and if one is generated, the ULA prefix
>> should be advertised to DHCPv6 PD clients, along with the GUA prefix.
>>
> Yes, that isn't supported in the current model.  I will update it to
> support this.
>
>
>> That aligns with the design intent of ULA to be used "inside of a more
>> limited area such as a site." But then we need to include logic that if you
>> receive an upstream ULA prefix, you SHOULD use it and not generate another
>> new ULA prefix if you are cascading CE Routers. If you want to create
>> separate requirements for ULA, that will work.
>>
> This is interesting point that I will need to give some thought too.
>
> My first thought is if a Router is advertising ULAs, say ULA-1. Then gets
> IA_PD for a different ULA, ULA-2 does it invalidate the ULA-1 and disrupt
> any connections between clients?
>

I would wait to invalidate the prefix and treat it as a renumbering event.
You would prefer the new ULA-2 prefix and change ULA-1 to not preferred; it
can remain valid for a few hours and then be invalidated. The downstream CE
Router should treat ULA-2 as its newly configured ULA prefix, remembering
it and using it even if the upstream switch disappears.

I hope that helps!
-- 
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David Farmer               Email:[e-mail]
Networking & Telecommunication Services
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