PPPoE unstable on I226-V (igc) in 26.7.4_1, fine on 26.7.3_11

[(MARLOO)]

After upgrading from 26.7.3_11 to 26.7.4_1, my PPPoE WAN on an Intel I226-V interface (driver igc) became unstable. The PPPoE session occasionally comes up and ping works, but the PPP daemon continuously logs LCP down events and reconnection attempts, leading to an unstable connection.

The root issue is physical link flapping on igc1 and igc3 (link state changed to DOWN/UP), not a PPPoE-only problem. PPPoE failures are a consequence of the unstable underlying link.

All four I226-V ports are already running NVM V2.32-0 (eTrack 0x80000425), confirmed via dmesg | grep igc.

------------Environment---------------------

OPNsense version:
FreeBSD 15.1-RELEASE-p3 stable/26.7-n283949-083dc7025377 SMP amd64 (26.7.4_1)

NIC: Intel Ethernet Controller I226-V (device 0x125c, rev 0x04)

Driver: igc (module pci/igc, interface igc3)

Physical interface: igc3 (MTU 1492, status: active, 1000baseT full-duplex)

PPPoE: pppoe0

------------------------------Hardware---------------------------------

Motherboard: Techvision TVI7309X

CPU: Intel Celeron N5105 @ 2.00 GHz (max 2.9 GHz)

Symptoms

PPPoE session comes up and obtains a public IP.

Ping to public IPs (e.g. 1.1.1.1) works while the session is up.

System logs show continuous PPPoE/LCP failures:


[opt12_link0] PPPoE connection timeout after 9 seconds
[opt12_link0] Link: DOWN event
[opt12_link0] LCP: Down event
[opt12_link0] Link: reconnection attempt N in X seconds
[opt12_link0] PPPoE: Connecting to ''

This loop repeats every ~9 seconds (PPPoE timeout after 9 seconds, then immediate reconnect). At the time of writing, the PPP daemon has performed over 130 reconnection attempts in less than an hour, with no sign of stabilization.

On 26.7.3_11, with the same hardware, cabling, and NVM V2.32 firmware, the connection is stable and no such LCP timeout loop occurs.

------------------------Questions-----------------------------------------------------

Is this a known regression in 26.7.4_1 related to the igc driver or PPPoE handling?

Are there any recommended workarounds (different MTU, driver options, sysctl tweaks) before downgrading back to 26.7.3_11?