VLAN Tagging on ISP Fiber: Why Your Router Won't Connect

If you've ever plugged your own router into an ISP fiber connection and gotten nothing but silence, you've encountered the mysterious world of VLAN tagging. This episode explains why ISPs require specific VLAN IDs on your WAN interface — it's not about making your traffic visible, but about tuning to the right "channel" inside the fiber. We break down the two common scenarios (ONT vs. direct SFP), the triple-play legacy that created this architecture, and the weekend-destroying failure modes: VLAN mismatch, MAC address locking, PPPoE credential issues, and missing DHCP options. Whether you're a home user or running a small business connection, understanding how ISPs segment their access networks will save you hours of debugging.