Last Modified: Apr 09, 2026
Affected Product(s):
BIG-IP TMOS
Known Affected Versions:
21.0.0, 21.0.0.1
Opened: Mar 29, 2026 Severity: 4-Minor
Public F5 documentation states that Link Controller (LC) is no longer available beginning with BIG-IP v21.0.0; however, systems upgraded from pre-21.x releases to v21.x with Link Controller provisioned: -- Successfully load existing LC configuration -- Show no warnings or errors during or after upgrade -- Display LC links as up/green -- Correctly respond to WideIP/DNS queries -- Successfully pass traffic This creates a discrepancy where Link Controller appears operational in v21.x, despite documentation indicating it is no longer available.
-- Unexpected loss of traffic steering or DNS-based decision logic - -Service disruption in future releases where LC functionality may be fully removed -- Lack of engineering support or fixes for LC-related issues
-- BIG-IP software version 21.x -- System upgraded from a pre-21.x release where Link Controller was previously supported -- Link Controller was provisioned before the upgrade -- Existing Link Controller objects are present (links, monitors, WideIPs) -- No explicit de-provisioning of Link Controller performed post-upgrade -- BIG-IP hardware platforms historically supporting Link Controller
Do not deploy new BIG?IP v21.x systems with Link Controller
None