PPPoE: Problems getting an IPv6 address on reconnection and other problems

[w0w]

Some other bug or feature found, or maybe I did something wrong

For example, I put pppoe0 down by issuing ifconfig pppoe0 down:

pppoe0: flags=8810<POINTOPOINT,SIMPLEX,MULTICAST> metric 0 mtu 1492
	description: WAN
	options=0
	inet6 fe80::d250:99ff:fec1:71b%pppoe0 prefixlen 64 scopeid 0x11
	groups: pppoec
	nd6 options=121<PERFORMNUD,AUTO_LINKLOCAL,NO_DAD>

And then I see default route still the same

IPv6 Routes
::/0	fe80::669e:f3ff:fe94:dd00%pppoe0	UGS	29	1492	pppoe0	

By the way, I don’t see fe80::669e:f3ff:fe94:dd00 anywhere.
Expected behavior is switching to another gateway on the WAN2, ex tier2

[stephenw10]

Hmm, does the gateway show as down? Anything logged?

[w0w]

@stephenw10
Pending. Shouldn’t it be in a pending state only when PPPoE is up but not yet connected?

@stephenw10 said in PPPoE: Problems getting an IPv6 address on reconnection and other problems:

Anything logged?

Unfortunately I've already destroyed pppoe0 so no logs currently, but I'll try to reproduce it later and see what do we have in the logs.

[stephenw10]

It depends how the gaterway is defined but if it's dynamic like that then, yes, I'd expect it to not show as pending.

Do you see the same thing of you disconnect the pppoe via the Interfaces Status page? Downing the interface manually is not something that would usually happen.

[w0w]

@stephenw10 said in PPPoE: Problems getting an IPv6 address on reconnection and other problems:

Do you see the same thing of you disconnect the pppoe via the Interfaces Status page?

Yes, it is showing "pending" even if I disconnect it via GUI.

[w0w]

Something tells me that all the issues with obtaining IPv6 addresses come from the fact that I’ve got a multi-WAN setup, and I’m using IPv6 on both links (different subnets). Because, if we look at the scenario where the WAN PPPoE interface doesn’t get an IPv6, I simply open the WAN2 interface—where both IPv4 and IPv6 addresses are picked up automatically by DHCP—click “Save” and “Apply” without changing anything (which effectively just runs the reconfigure script), and after that I suddenly get an IPv6 on the WAN PPPoE… Very strange, isn’t it?

All right, so I go back into WAN2’s settings again, disable IPv6 completely, set the default route to “Automatic,” delete the failover gateway, and remove the remaining DHCPv6 gateway.

Then I flip CARP into maintenance mode and end up with the following picture (note the WAN2 interface).

Why am I getting an IPv6 address on WAN2 when it’s clearly set to “None”?
I think someone else needs to test a multi-WAN setup with IPv6 enabled on at least two WAN interfaces and one is PPPoE, and I don't think CARP is needed.

[stephenw10]

Hmm. Well that's interesting.

Is that IPv6 address you're getting on WAN2 correct for WAN2? Or is it somehow applying the PPPoE v6 address there?

[w0w]

@stephenw10
No, that’s the correct address for WAN2 when DHCPv6 is enabled. It has only happened once in my tests so far, and I haven’t run long-term tests yet—I need the network up right now. The next time I can experiment will be tomorrow morning.

[w0w]

The glitch where an IPv6 address appeared on WAN2 even though IPv6 was disabled on that interface hasn’t happened again after I simply hit Save & Apply with no changes.

I’ve now booted into version 23.09.1. From what I can see, the key difference in the GUI is how interface status is reported: in 23.09.1 the interface stays down until the PPPoE session is actually established by mpd5, whereas in 23.05 the interface flips to UP as soon as the virtual pppoe0 device gets the UP flag—even though the PPP session hasn’t finished negotiating. I don’t think this behaviour affects anything functional, but it is worth noting.

At this point my working theory is that the problem only occurs when both WAN links use DHCPv6. If I switch WAN2 to SLAAC (which is also an option), the disconnect/connect cycle works fine and I don’t see any issues.

[stephenw10]

Hmm, yes if_pppoe shows as up as soon as it starts to try to connect. If that is the case you should also not see it when running mpd5 in 25.03.

[w0w]

@stephenw10
No, I'm not sure whether the up/down state affects the receiving of IPv6 addresses or not. I can certainly test it with mpd5 just in case, but later. If no one else is having issues in a multi-WAN configuration where both WANs receive IPv6 via DHCP, then I'm fine with switching the second WAN to an alternative configuration using SLAAC only.

[stephenw10]

It's not something I've heard from anyone else. I know at least one of our devs has dual pppoe WANs with IPv6 on both.

[w0w]

@stephenw10 said in PPPoE: Problems getting an IPv6 address on reconnection and other problems:

dual pppoe WANs with IPv6 on both.
DHCP?

[stephenw10]

DHCPv6 over PPPoE. The usual PPPoE setup.