The basic idea
On a shared fabric, each customer’s connections must stay separate. Ethernet does this with VLAN tags defined by IEEE 802.1Q. Every frame carries a small tag with a VLAN ID, and switches use that ID to keep traffic in its own lane.
On your port
When you order virtual circuits on a Peer1IX port, each circuit is assigned a VLAN ID on your side. Your router sends traffic for the cloud on one VLAN, traffic for a partner on another, and peering on a third.
Inside the fabric
The fabric maps each of your VLANs to an isolated path to its destination. Your VLAN IDs only have meaning on your port; other customers can use the same numbers without conflict.
QinQ for transparency
Sometimes you want to carry your own internal VLANs across a circuit unchanged. QinQ (802.1ad) adds an outer service tag around your customer tag, so the fabric can transport your VLANs transparently.
Tips for a clean design
- Reserve VLAN ranges for different service types.
- Document every VLAN with its purpose and destination.
- Use consistent sub-interface naming on routers.
- Remove unused VLANs promptly.
A little planning keeps a hub with dozens of connections easy to operate.
