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

[Timothy Winters <[e-mail]>]

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?

>
>

> Also, I would like SNAC routers to use the ULA prefix from the upstream CE
> Router instead of generating a new ULA prefix if a ULA prefix is advertised
> for local communications when the ISP GUA prefix is unavailable.
>
> Is there a reason for PD-per-device to not behave similarly?
>
> Thanks.
>
> --
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