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VLANs and L2

How to see which VLANs a trunk allows

A VLAN reaches a remote switch only if every trunk along the way allows it, so when a VLAN is missing at one site the allowed list is the first thing to check. The Ports inventory shows the allowed VLANs and the native VLAN for every trunk in the estate, side by side.

All the questions
The same procedure as a recording, subtitled in English and French. This recording predates the latest revision of the steps: it opens on a screen the written guide no longer includes.
Before you start

What you need

  • Module required: inventory.
  • Permission required: view_inventory.
  • all

1. Open Inventory then Ports

app.nactrack.com/inventory/interfaces
Open Inventory then Ports
Open Inventory and choose Ports. Every physical and logical interface NacTrack collected is here, one row each, which is why the table is wide: it carries the VLAN, speed, duplex, media and VRF for each one.

2. Read the VLAN columns

app.nactrack.com/inventory/interfaces
Read the VLAN columns
Four columns answer the VLAN question. Access VLAN and Voice VLAN apply to access ports. Native VLAN and Allowed VLANs apply to trunks: the allowed list is exactly what the trunk will carry, and anything absent from it is silently dropped at that hop.
The limits

What this view does not tell you

  • A VLAN present in the allowed list is not necessarily defined on the switch. The allowed list is configuration text; it can name a VLAN that was never created, and the trunk will still carry nothing for it.
  • Nothing here counts the VLANs on a trunk or ranks trunks by how many they carry. The allowed list is shown as it was configured, and you read it yourself.

Try the same thing on your own estate

Request accessAll the questionsEvery guide as a PDF (25 MB)