Report "Delegated-IPv6-Prefix" attribute for PPPoE

[NathanA]

Back on 7 November 2022, I wrote:
`

So, I see now after testing a bit more that there is a problem. It’s actually not a problem with the 60 seconds, though. The problem is that, 10 seconds after lease renewal happens, the IP addresses assigned from the pool briefly go “invalid” and then back to “valid” again. At the same time, “IPv6 address changed” is logged, even if the addresses didn’t change at all. During this brief blip (1-2 seconds), forwarding of v6 traffic for those IPs on those interfaces is briefly interrupted.

This is Bad™. But it doesn’t just happen with the IPs that have 60 second lease time. It happens with any DHCPv6-assigned IPs, right after they are renewed. So even when you have 3 day lease times for PD prefixes, after 36 hours pass, there will be brief 1-2 second outage.

Stupid.

`
…but it turns out that I’m the one who was (is?) stupid.

I was experiencing this phenomenon because on my test client router, I was using my script to hackishly implement RFC 9096. RouterOS would run my script at every DHCP lease change event, even for a lease renewal where the address did not change. And my script would blindly disable and re-enable the IPv6 address whenever it would run. Since with DHCP most clients typically attempt lease renewal after half of the lease time has gone by, and since the lease time was 1 minute, I was seeing IPv6 internet reachability blips on my LAN every 30 seconds.

But it was my script causing this, not RouterOS.

I have rearchitected my script to not do this, and problem solved. So the lease time being only 60 seconds long is still effectively a non-issue. That said, for those who care about it, it looks like in ROS 7.7 MikroTik changed this so that the lease time is now 1 day for these dynamic DHCPv6 servers created in response to the Delegated-IPv6-Prefix reply attribute.