Re: [v6ops] A common problem with SLAAC in "renumbering" scenarios

[Mikael Abrahamsson <[e-mail]>]

On Thu, 31 Jan 2019, Fernando Gont wrote:

> Any comments will be welcome.

"   o  A CPE MUST record, on stable storage, the list of prefixes being
       advertised on each LAN segment."

This is not always doable as some devices have very small flash with no 
write-leveling, so doing this generally might ruin the flash cells on some 
devices. This above requirement will drive cost, especially in the low end 
market of HGWs.

       *  Any prefixes that were previously advertised via SLAAC, but
          that are not currently intended for address configuration, MUST
          be advertised with a PIO option with the "A" bit set to 1 and
          the "Valid Lifetime" and a "Preferred Lifetime" set to 0.

Doesn't RFC7084 already say this? L-13.

Another comment, typically the lifetime of the LAN PIO is capped at the 
DHCPv6-PD WAN lease time. I couldn't find this requirement in RFC7084, but 
I only searched for "lifetime". Anyhow, Openwrt does this and might be 
good to mention.

When the new prefix is received it'll most likely have a higher preferred 
and valid lifetime, so hosts should use the new prefix just by means of 
them preferring the higher preferred lifetime of that PIO. So the problem 
is a bit less than you write in the draft.

So while I am generally sympathetic to this draft and what it tries to 
achieve (especially the part where it ties the router announcing something 
to what it's later announcing, and lack of something means it's implicitly 
zero preferred time for that), we need to figure out a few more things 
first. RFC7084 was informational which made it fairly easy to get through, 
now you're proposing a standards track document so we need to make sure 
everything works. Changing all hosts is a big thing.

-- 
Mikael Abrahamsson    email: [e-mail]