Comment by cyberax
2 days ago
Not really. Believe it or not, but the initial plan for IPv6 was to NOT have the PI blocks at all. Everyone was supposed to use PA (Provider Aggregated) blocks.
The needs for dual-homing and failover were completely glossed over in the IPv6 design, and the IETF has not acknowledged these needs even to this day.
They weren't glossed over. Dual-homing is handled in RFC 3484 (https://datatracker.ietf.org/doc/html/rfc3484#section-5 under rule 5) and ND is designed to detect unreachable routers and stop using them (see e.g. https://datatracker.ietf.org/doc/html/rfc1970#section-6.3.6). You can also specify router preference in RAs (https://datatracker.ietf.org/doc/html/rfc4191).
They thought about these things and put features into the protocol to support them. This is, once again, the opposite of your belief that they didn't.
"PA" or "PI" is an administrative distinction and technically has nothing to do with BGP or multi-homing. You can still announce PA blocks under your own ASN. I do that today, actually.
It's the same with IPv4, by the way. An ISP can assign you a block from their allocation, you can still announce it with your own ASN as long as it doesn't violate the issuing provider's policy, you're still a customer, etc.
It does have the effect of requiring you to follow the upstream ISP's numbering system. So if they switch the prefix, you have to follow.
And it's more of the "it's the thought that counts" thing. Multihoming was considered to be something rather exotic and mostly a requirement for ISPs or large companies.
Yes, but that rarely happens with IPv6. ISP / LIRs get huge allocations.
The real problem is BGP isn't available from most home or "small business" internet connections. You can't multihome even if you want to. You need a DIA / enterprise plan, or you need to use tunneling (which is what I do, from several BGP capable VPSes, in a configuration that is too complex for the typical SMB.)