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

[Ted Lemon <[e-mail]>]

SNAC already prefers a DHCPv6-assigned prefix (ULA or GUA) to its own
locally-generated prefix.

On Wed, Jul 24, 2024 at 9:39 AM David Farmer <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? Does that mean that if you
> implement CPE-lan-pd, you no longer have ULA on even the CE router's local
> interfaces?
>
> 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. 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.
>
> 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.
>
> --
> ===============================================
> David Farmer               Email:[e-mail]
> Networking & Telecommunication Services
> Office of Information Technology
> University of Minnesota
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