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

[David Farmer <[e-mail]>]

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.

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