[v6ops] Re: router lifetime and coupling prefix/route (was Re: Re: I-D Action: draft-ietf-v6ops-rfc7084bis-06.txt)

[Mikael Abrahamsson <[e-mail]>]

On Wed, 8 Jul 2026, Brian E Carpenter wrote:

> Remember that 8504(bis) is "IPv6 Node Requirements" and according to 
> RFC8200, a node is "a device that implements IPv6." But you're right, of 
> course. I think we have to read RFC 8028 as applying to any node that is 
> acting the role of a host, even if it's also a router.

I did some more thinking to distill down what I think is doable for 
7084bis and which would solve most of what I want to solve.

RFC 4191 Router Preference already solves the primary/secondary default 
router selection, and 8504bis makes Type C a MUST. But 7084bis doesn't 
require CE routers to make the Router Preference field configurable on the 
LAN side.

My scenario: two CE routers on the same LAN, one fiber one mobile. I want 
hosts to prefer the fiber router's prefix and default route, and fall back 
to the mobile one when fiber is down. RFC 4191 Router Preference handles 
the default router part. But there's no coupling to address selection — 
RFC 6724 doesn't know about router preference. Configurable PIO preferred 
lifetimes would let me make the secondary's prefix less preferred, as a 
workaround.

So the asks for 7084bis in that case:

1. CE routers SHOULD allow configuration of the Router Preference field 
RFC4191 in Router Advertisements on their LAN interfaces.

2. CE routers SHOULD allow configuration of the maximum advertised PIO 
Preferred and Valid Lifetime on their LAN interfaces, capped to the 
remaining WAN-side delegated prefix lifetime per L-15.

3. CE routers SHOULD allow configuration of the maximum IA_PD preferred 
and valid lifetimes for prefixes delegated on the LAN side, capped to the 
remaining WAN-side delegated prefix lifetime per LPD-10.

4. CE routers SHOULD allow configuration of the maximum IA_NA preferred 
and valid lifetimes for addresses assigned on the LAN side, capped to the 
remaining WAN-side delegated prefix lifetime per L-15.

These knobs would allow an end-user to configure multiple CE routers on 
the same LAN to prioritise one connection over another, across all 
addressing and routing mechanisms.

-- 
Mikael Abrahamsson    email: [e-mail]