Using TACACS+ on Big-IP LTM

Check the routing on the management interface.

 

 

Unsolicited traffic (like tacacs+) will be sourced from whatever IP has the lowest cost route to the destination. If you just have a default route configured on the mgmt interface, and a default route on the tmm side, the tacacs+ traffic will source from the TMM side interface (since TMM routes are lower cost than management). An easy way to test would be to create a host route on the management interface to the TACACS server and see if that resolves the problem.