If you actually want that topology, I think in practice the downstream router (B) must be at least a /64; if you got a /48 then I think you can set up A with /56s, which it can use to sub-allocate a /64 to B.
https://tools.ietf.org/id/draft-ietf-homenet-arch-01.html The config in section 7.2 of https://wiki.archlinux.org/title/IPv6#Prefix_delegation_(DHCPv6-PD) might be what you're looking for? (See the note about `sla-len`.) On Sun, Jun 27, 2021 at 12:05 PM Kristian McColm < [email protected]> wrote: > RFC 5375 advises against prefixes longer than /64. > > https://datatracker.ietf.org/doc/html/rfc5375#appendix-B.2 > > A /48 gives you 65535 /64’s, why not use some of them? > > ------------------------------ > *From:* [email protected] > <[email protected]> on > behalf of Doug Hardie <[email protected]> > *Sent:* Sunday, June 27, 2021 2:54:01 PM > *To:* [email protected] <[email protected]> > *Subject:* Prefix delegation to sub nets > > I am trying to setup an IPv6 environment. There is a primary router (A) > that receives a /48 prefix via DHCP6 from the ISP. That router configures > itself properly via dhcp6c. It also creates 2 LAN /64 prefixes and creates > EUI-64 addresses on the two LAN interfaces. One of those interfaces is > connected to a second router (B), among other devices. The B router > receives the prefix via SLAAC and creates its own EUI-64 address. However, > that router needs to create a smaller subnet, /72, and distribute it to the > devices on that LAN. I have not been able to figure out how to make that > happen. > > Clearly, manual configuration would work, but the prefix received from the > ISP can change which would raise havoc with the network. I suspect that > dhcp6s needto be run alongside dhcp6c on router B and then the other > devices run dhcp6c. However, I don't see how to get the prefix that dhcp6c > receives on router B to the dhcp6s process on router B. I believe I am > missing something, but haven't been able to find it. Thanks, > > -- Doug > > > > > > ------------------------------ > This communication is confidential. We only send and receive email on the > basis of the terms set out at www.rogers.com/web/content/emailnotice > > > > Ce message est confidentiel. Notre transmission et réception de courriels > se fait strictement suivant les modalités énoncées dans l’avis publié à > www.rogers.com/aviscourriel > > ------------------------------ > -- Michael Chang
