F5OS VLAN naming length restrictions

Hi Stefan_Klotz​ ,

Thank you for your detailed inquiry.

I have reviewed the VLAN naming behavior on your environment (F5OS 1.8.3 with BIG‑IP 17.5.1.3), and based on my findings i can  share that what you are observing is expected and normal system behavior.

F5OS and BIG‑IP tenants follow different naming constraints:

The BIG‑IP tenant layer (TMOS‑based) enforces a maximum VLAN name limit of 31 characters.

When a VLAN is pushed from F5OS into a tenant, F5OS automatically:

Truncates the VLAN name to meet the TMOS limit

Appends a system‑generated suffix in the format:

“-T<VLAN‑ID>.0”

This ensures each VLAN name remains unique within the tenant environment.

And this is not a defect or BUG,  this is functioning as designed.

The naming restriction comes from TMOS, not F5OS, and the automatic truncation is the expected compatibility behavior.

For reference, F5 documents these TMOS naming constraints here:

Reference

K16539386: VLAN name with more than 31 characters causes issues for F5OS BIG-IP tenants such as mcpd errors and config load failure

https://my.f5.com/s/article/K16539386

Recommended Actions

Use VLAN names that are a maximum of 31 characters to avoid this issue.

To recover from the problematic state:

• Ensure VLANs are no longer than 31 chars in F5OS and tenant's bigip_base.conf
• Any references to renamed VLANs should be updated in the bigip_base.conf as needed
• Reload config via mcpd forceload (K13030)
• Upgrade to a version with the fix for bug ID1183901

HTH

Best regards

F5 Design Engineer