GL-MT6000 (Flint 2) WAN link flapping on Sky FTTP (Ireland) – Sky router works fine

Router
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Hi all,

I’m having a persistent WAN link flapping / disconnecting issue with a GL-MT6000 (Flint 2) when used directly with Sky Broadband FTTP in Ireland, and I’m hoping someone here (or GL.iNet staff) can advise.

Setup

  • ISP: Sky FTTP (Ireland)

  • ONT: Sky-provided fibre ONT

  • Router: GL.iNet GL-MT6000 (Flint 2)

  • Connection: ONT - Flint 2 (tested both dedicated WAN and WAN/LAN1)

behaviours

  • WAN Ethernet continuously flaps (connect / disconnect)

  • PPPoE never completes because the physical link is unstable

  • This happens:

    • With a clean config

    • With PPPoE (sky / sky, MTU 1492)

    • With and without MAC cloning

    • On both WAN ports

    • After full ONT power cycles (5–15 mins)

Plugging the Sky router back into the ONT works perfectly. Power and PON LEDs on the ONT are solid green This strongly suggests the fibre line and ONT are healthy

  • PPPoE credentials (are these correct in Ireland)

  • Cabling (multiple known-good Cat6 cables tested)

  • Multi-WAN / failover

  • MAC binding (Sky router MAC cloned successfully)

  • Firmware reset / clean setup

Both WAN ports on the Flint 2 negotiate at 2.5 Gbps, and there appears to be no way to force 1 Gbps on the WAN interface.

It looks like a PHY / auto-negotiation compatibility issue between the Sky ONT and the Flint 2 Ethernet chipset.

does anyone know:

  1. Is this a known interoperability issue between the GL-MT6000 (2.5G WAN) and certain Sky/Openreach ONTs?

  2. Is there any supported way (UI, LuCI, or CLI) to force the WAN port to 1 Gbps Full Duplex on the MT6000?

  3. Has anyone successfully used a Flint 2 directly on Sky FTTP Ireland without placing the Sky router in front?

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