core: IPv6 connection is lost on the LAN interface after the tracked WAN interface (PPPoE) reconnected

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Describe the bug With the update from 20.1 to 20.7 the IPv6 issues got worse for the case when the PPPoE WAN connection is lost and reconnected. Whenever the VDSL Sync was lost and the PPPoE had to re-establish the connnection the IPv6 connection (except link local for sure) is gone on the LAN interface that is tracking the WAN (VDSL) interface.

In the past I had the same issue but it was not happening all the time and if it happened the workaround was to run /var/etc/rtsold_pppoe0_script.sh thanks to a hint from Franco F. This doesn’t fix it anymore.

My current manual workaround is to go to the UI and go to the LAN Interface, don’t change anything, just press “Save” and apply so that the interface is reconfigured with the same settings and IPv6 connection is back and now also for the clients in my network.

To Reproduce Steps to reproduce the behavior:

1. Wait for (or trigger) PPPoE disconnect
2. Wait for established PPPoE link
3. See IPv6 on WAN working but not on LAN interface
4. Reconfigure LAN interface to get it working again

Expected behavior

Stable IPv6 connection, even after WAN reconnects.

Screenshots

Relevant log files

Let me know which ones are necessary.

Additional context

I’m willing to debug and manually add additional debug infos if it helps. I’m trying to understand how the different parts interact with each other with regards to IPv6.

Since it’s “fixed” by manually triggering LAN interface reconfigure I would guess that configuration is fine but that the tracking between WAN and LAN interface has some bigger issue now. So feel free to guide me into which files I should look.

WAN (VDSL) interface is configured for IPv6 like this:

IPv6 Configuration Type - DHCPv6 Configuration Mode - Basic Request only an IPv6 Prefix - Checked Prefix Delegation Size - 56 Send IPv6 Preifx hint - Checked Use IPv4 connectivity - Checked

LAN interface configuration for IPv6:

IPv6 Configuration Type - Track Interface Track IPv6 Interface - VDSL (Name of the WAN interface in my setup) IPv6 Prefix ID - 0x24

Environment

OPNsense 20.7.1-amd64 AMD GX-416RA SOC (4 cores) OPNsense A10 Quad Core SSD Desktop Gen2

Thanks!