What is the registration (in Option 43 mode) procedure when an AC and a Fit AP are connected across a Layer 3 network

When connecting to an AC across a Layer 3 network, a fit AP registers with the AC based on the AC IP address carried in Option 43 of a DHCP packet. The right figure shows the registration procedure.
The registration procedure is as follows:
1. The fit AP obtains an IP address and Option 43 from the DHCP server. Option 43 contains the AC IP address, gateway IP address, and DNS server IP address.
2. The fit AP sends a unicast Discovery Request message to an AC based on the AC IP address carried in Option 43.
3. After receiving the Discovery Request message, the AC checks whether the fit AP has the access right. If the fit AP is authorized, the AC replies with a Discovery Response message.
4. The fit AP downloads the latest software version from the AC.
5. The fit AP downloads the latest configurations from the AC.
6. The fit AP exchanges service data packets with the AC.