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Stefan_Klotz's avatar
Stefan_Klotz
Icon for Cumulonimbus rankCumulonimbus
Jan 09, 2026

F5OS VLAN naming length restrictions

I must notice, that there seems to be a length restriction when creating VLANs on F5OS.
I'm allowed to enter long names on F5OS-level without any warnings or errors, but when assigning them to a tenant, the name within the tenant will be truncated if its longer than 31 characters.
It looks like this, means there is a suffix in the format of "-T<VLAN-ID>.0"

On F5OS-level it looks like this:

Is this a normal behavior? Can or will this be fixed?
And are there any other such restrictions for other configuration items?
For your reference, we are running F5OS 1.8.3 and BIG-IP 17.5.1.3.
Thank you!

Regards,
Stefan :)

 

F5OS
rseries
vlan

3 Replies

  • Melissa_C's avatar
    Melissa_C
    Icon for Moderator rankModerator
    Jan 22, 2026

    Hello Stefan_Klotz​ 

    Noticed this has been up for some time with no response, were you able to get answers outside of DevCentral that you would be able to provide an update on? It not let me know and I can try to find someone who may know the answer or can get you in the right direction. 

    -Melissa 

    • Stefan_Klotz's avatar
      Stefan_Klotz
      Icon for Cumulonimbus rankCumulonimbus
      Jan 27, 2026

      Dear Melissa,
      no, I don't have an answer here yet.
      Just want to let you know, that I "found" something and want to double check if this is already known (and planned to be fixed) or not.
      Or if there is maybe a technical reason for this limitation, which can't be fixed.
      But then it would be great, if you could adjust your documentation and highlight this limitation.
      Thank you!

      Regards,
      Stefan

  • F5_Design_Engineer's avatar
    F5_Design_Engineer
    Icon for MVP rankMVP
    Jan 28, 2026

    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