Re: Understanding IPv6-PD over PPPoE

On 15/06/2021 18:19, Bjørn Mork wrote:

Yes, that is buggy.  I wonder... I did hit a similar issue many many
years ago while testing IPv6 over PPPoE (which we didn't end up doing in
the end).

I'm not entirely sure how the default route is assigned - on ethernet it would be assigned on receipt of the router advertisement, but is that still the case with PPP, or is the default route negotiated by IPv6CP?

Maybe you are hitting something similar with your ISP?  The typical
symptom would be that DHCPv6 worked once again after the lease expires.
If this is the issue, then you can probably assign a static interface-id
on your end to work around it.

I've got 2 internet connections on the same ISP.

One of them was set up years ago and the ISP was trialling IPv6 at the time, so I requested an IPv6 prefix. This one is working ok (the DHCPv6 advertise contains my prefix). I have no idea whether the ISP ever rolled out IPv6 to everyone by default, but this works for me since I enrolled on the trial years ago.

The other connection is new. The ISP sends router advertisements and we get a default route, but the DHCPv6 advertise doesn't contain a prefix or IP. I think it's a reasonable assumption that the ISP never enabled IPv6 for everyone by default and the result is that when you send a DHCPv6 solicit you don't get a prefix on this connection.

I think it would be too risky to try to be smart here.

How can the system know whthere there will be an address available
later?  Should it cache all the routing?  What if the system has an
address which isn't routable on the interface with the default route?

Installing the routes you receive is the only sane thing to do, IMHO.

But it results in a configuration that causes real-world brokenness (long timeouts waiting for connections that can never happen).

The correct thing would probably be for the kernel to treat all global addresses as unroutable if the machine only has link-local addresses, irrespective of the existence of a default route. Is there a reason why you would ever want to generate traffic with a link-local source address and a global destination address?

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