Re: there should be a ULA prefix?? [was: A common problem with SLAAC in "renumbering" scenarios]

[Alexandre Petrescu <[e-mail]>]

Le 26/02/2019 à 23:10, Mark Smith a écrit :
> 
> 
> On Wed., 27 Feb. 2019, 06:36 Brian E Carpenter, 
> <[e-mail] <mailto:[e-mail]>> wrote:
> 
>     Philip,
> 
>     On 26-Feb-19 23:33, Philip Homburg wrote:
>      >> So given that document is 12 years old, with that default copied
>     from one that
>      >> is 21 years old, is an update required?
>      >>
>      >> And if so, to what?
>      >
>      > I think this should be updated.
>      >
>      > A long time ago, the model was that you would get a prefix from
>     your ISP
>      > and that was the only global prefix on the local network.
>      >
>      > So with short lifetimes, if the internet connection would go down
>     for a
>      > relatively long period, there would be no global prefix anymore
>     and hosts
>      > would have to resort to link local to communicate (which
>     obviously fails
>      > if there are multiple subnets).
>      >
>      > Some time in the past, the thinking changed and now there should
>     be a ULA
>      > prefix in addition to any global prefixes.
> 
>     Really? Where do you think that is stated?
> 
>     I happen to run my CPE with ULA enabled, but I'm not aware of any
>     recommendation to do so.
> 
> 
> RFC7084. Was also in its ancestor.
> 
> OpenWRT is enabling ULAs by default (although with infinite lifetimes 
> which is something that should be changed).

YEs I confirm openwrt is enabling ULAs by default.

In recent years I tested several IoT-class cellular router owrt devices 
and they all enable ULAs by default on their WiFi and Ethernet 
interfaces.  In some cases they also enable NAT IPv6.  These owrt dont 
enable 64share nor CLAT; these latter are typical on Android (a 
different OS distribution than owrt, both based on linux kernel) and on 
Apple iOS (OS distribution based on mach kernel?).

While these IoT-class routers are not perfect, their use of ULAs is not 
a culprit.  ULA is fine.

It's their reliance on 64share (an INFORMATIONAL RFC), IPv6 NAT 
(perpetuates the NAT problem) and rigid length 64bit IIDs that are culprits.

A more reasonable IoT-class cellular router would use variable length 
IIDs, and DHCPv6 Prefix Delegation (Stds Track).

> Back in 2010 Fritzboxes were doing ULAs too, although badly. They had 
> all zeros random parts, and were trying to swap them in and out with the 
> PD GUA addresses as the WAN link went up or down. (It seemed they didn't 
> understand the fundamental idea that IPv6 supports multiaddressing.)

Yes I heard of several German cellular router devices enabling ULAs.

Alex

> 
> 
> 
> 
> 
>      > So I think that with a ULA, it makes more sense for a CPE to
>     limit lifetimes
>      > to some multiple of the RA interval.
> 
>     Why? I don't expect my ULA prefix to change ever. Or do you mean the
>     lifetimes
>     for globally routeable prefixes?
> 
> 
>         Brian
> 
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