Figure 2-4 shows 6 routers and 1 controller. R1, R2, R3, and R4 belong to AS-100 and R5 and R6 belongs to AS-200, Controller belongs to AS-300 R1 and R2 has an iBGP (BGP-LS) session with R3. R3 and R5 have an eBGP session with the controller with BGP-LS.