A Cisco 5520 WLC has management IP 172.16.50.5. CAP2802I APs on VLAN 100 (172.16.100.0/24) fail to join when DHCP option 43 is set as ASCII 172.16.50.5. Which action resolves the issue?

The correct answer is to configure option 43 as hex F104.AC10.3205. Cisco Lightweight Access Points (LAPs) require DHCP Option 43 to be configured in a specific hexadecimal format for WLC discovery. The format is Type + Length + Value. For a single WLC IP address, the Type is F1, the Length is 04 (for 4 bytes in an IPv4 address), and the Value is the hexadecimal representation of the WLC's IP address. The WLC IP 172.16.50.5 converts to AC.10.32.05 in hexadecimal. Therefore, the correct Option 43 string is F104.AC10.3205. Configuring option 43 as hex F104.CA10.3205 is incorrect because CA is not the hexadecimal equivalent of 172. Configuring a DNS server (172.16.50.5 or 172.16.100.1) is a valid AP discovery method if the WLC has a DNS entry, but it's not the solution for a misconfigured Option 43. The question specifically states that Option 43 is set but failing, indicating an issue with its format, not the absence of a discovery method.