Subj : Two ISPs and backup for a home network (dual-homing)
To   : Dmitry Protasoff
From : Victor Sudakov
Date : Sun Jul 04 2021 12:36:40

Dear Dmitry,

01 Jul 21 16:46, you wrote to me:

 VS>> The original IPv4 was also miserable with its classful networks,
 VS>> RIPv1 etc. I still cannot imagine however what "real life"
 VS>> problem they are solving by creating NAT for ipv6.

 DP> For example - rerouting traffic via VPN to get thru RKN's DPI.
 DP> Real life scenario :)

Why would you need NAT for that? Get a VPN/tunnel provider who offers a global /64 or /56 or even a /48, like HE does.

 DP>>> translation. It's much more lightweight and easy to implement.

 VS>> Either you translate only the higher 64 bits of the address, or
 VS>> the whole 128 bits of the address, you still rewrite the packet.
 VS>> True, you don't do PAT, that's why I said that it looks like a
 VS>> one-to-one IPv4 NAT (much like in AWS VPC "public" subnets).

 DP> Yeah, but you can have "host" part the same for several uplinks and
 DP> change prefix only on NPTv6 gateway. It's the best ipv6 can offer for
 DP> you, sorry.

Too bad and a bit unexpected. There are/were rather complex things like Mobile IPv6 and HMIP, and they have not thought of a simple failover?

 VS>> Nope, but I think $subj can be implemented today, e.g. via some
 VS>> field in RAs etc. In FreeBSD (and I'm sure in other IPv6
 VS>> implementations) you can select the prerred source address, you
 VS>> only have to add some way to change it automatically when a "dead
 VS>> gateway" is detected.

 DP> It adds more complexity and cannot be implemented easily in userland
 DP> across multiple OSes.

OK, let's start anew with a simple setup. If there are two routers in a home LAN advertising different global prefixes, and one of them goes offline, will IPv6 end hosts detect that and remove the corresponding addresses from their configuration?

Victor Sudakov, VAS4-RIPE, VAS47-RIPN
--- GoldED+/BSD 1.1.5-b20170303-b20170303
 * Origin: Ulthar (2:5005/49)

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