When connecting to an AC across a Layer 3 network, a Fit AP registers with the AC based on the AC IP address resolved by the DNS server. The following figure shows the registration procedure.
The registration procedure is as follows:
1, The Fit AP obtains its own IP address, AC domain name (through DHCP Option 15), DHCP server IP address, and DNS server IP address from the DHCP server.
2, The Fit AP starts the CAPWAP discovery mechanism and broadcasts Discovery Request messages to associate with an AC. The Fit AP may take either of the following actions if no response is received after multiple discovery attempts:
If the DHCP server supports Option 15 and adds Option 15 in the response message (to allocate an IP address), the AP obtains the AC host name list from Option 15 and sends a message to the DNS server to request for the corresponding AC IP address list. After obtaining the AC IP address list, the AP sends Discovery Request messages to obtain the IP addresses of the ACs in the AC host name list from the DNS server. After obtaining the IP addresses of the ACs, the AP sends Discovery Request messages to the ACs one by one.
If the DHCP server does not support Option 15, it sends domain name HW.xxxx.xxx to the AP. The AP obtains the IP address of HW.xxxx.xxx from the DNS server. Then the AP sends a Discovery Request message to this IP address.
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 user data packets with the AC.