[v6ops] Re: [dhcwg] Re: Re: [IPv6]Re: Android now supports DHCPv6 PD

[Daryll Swer <[e-mail]>]

>
> People who solve every problem by pushing the complexity resulting from
> their choices to others want to use delegated /64s so they can run SLAAC on
> containers and VMs, and we keep wasting everyone’s time bikeshedding the
> resulting FUBAR instead because we’re not willing to collectively tell them
> to fix their stuff.


I'm no Android/Google or SLAAC fanboy (I think people know that on this
list), but making the smallest subnet a /64 just simplifies your overall
subnet hierarchy (hopefully in your Netbox and for some in Excel sheets),
it's just cleaner, and you can aggregate the /64s to some parent subnet
which solves the FIB/TCAM scale topic as mentioned a few times on this list.

I don't think SLAAC (at least for those of us who are pro-routing, BGP to
the host, ia_pd as a poor-man's routing protocol et al.) is the primary
factor/reason to do /64s, IMO, the primary factor/reason is minimisation of
your subnet plan from fragmentation, especially as the business ages, teams
changes, MGMT changes, etc. A well-done+documented v6 plan tends to be
better in the long run, and I can confidently make this statement after
having dealt with IPv6 re-architecture for orgs that deployed IPv6 from
2007+ era. Subnet planning is important, /64s just makes it simpler.

I think the only place where I've heard of SLAAC being used on host-like
networking is the Thread/Matter/IoT stuff with a /64, but excluding this
one, SLAAC isn't the decisive factor for doing /64 minimum (per host and
per-link-interface).

*--*
Best Regards
Daryll Swer
Website: daryllswer.com
<https://l.shortlink.es/l/b59dbe349aa48862c20a83ae5600322c91b3110a?u=2153471>


On Thu, 18 Sept 2025 at 20:08, Ivan Pepelnjak <[e-mail]> wrote:

> It's certainly not the most compelling reason. The most compelling reason
> is that it makes life easier for leaf routers, since they generally only
> have to track the prefix, and not individual IP addresses.
>
>
> Oh, DHCP-PD is a wonderful thing.  Insisting on /64 is what makes this
> annoying, because it creates needless pressure on the left side of the
> address plan.
>
>
> Sane people assign /80 to IPv6 hosts that need multiple addresses:
>
>  https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-prefix-eni.html
> <https://l.shortlink.es/l/f65f086e83c652d3a1e0d14b407a91539f62aff2?u=2153471>
>
> Needless to say, that allows you to use 2^48 hosts within the /64 prefix
> without changing anything on the routing side.
>
> People who solve every problem by pushing the complexity resulting from
> their choices to others want to use delegated /64s so they can run SLAAC on
> containers and VMs, and we keep wasting everyone’s time bikeshedding the
> resulting FUBAR instead because we’re not willing to collectively tell them
> to fix their stuff.
>
> Whatever,
> Ivan
>