350-401 · Question #308
An engineer has deployed a single Cisco 5520 WLC with a management IP address of 172.16.50.5/24. The engineer must register 50 new Cisco AIR-CAP2802I-E-K9 access points to the WLC using DHCP option 43
The correct answer is A. configure option 43 Hex F104.AC10.3205. Explanation Option A is correct because Cisco access points require DHCP Option 43 to be encoded in a specific hexadecimal TLV (Type-Length-Value) format, not plain ASCII. The correct hex string breaks down as: F1 (type/suboption for Cisco WLC), 04 (length = 4 bytes for an IPv4 a
Question
An engineer has deployed a single Cisco 5520 WLC with a management IP address of 172.16.50.5/24. The engineer must register 50 new Cisco AIR-CAP2802I-E-K9 access points to the WLC using DHCP option 43. The access points are connected to a switch in VLAN 100 that uses the 172.16.100.0/24 subnet. The engineer has configured the DHCP scope on the switch as follows:
Network 172.16.100.0 255.255.255.0 Default Router 172.16.100.1 Option 43 ASCII 172.16.50.5 The access points are failing to join the wireless LAN controller. Which action resolves the issue?
Options
- Aconfigure option 43 Hex F104.AC10.3205
- Bconfigure option 43 Hex F104.CA10.3205
- Cconfigure dns-server 172.16.50.5
- Dconfigure dns-server 172.16.100.1
How the community answered
(36 responses)- A81% (29)
- B11% (4)
- C3% (1)
- D6% (2)
Explanation
Explanation
Option A is correct because Cisco access points require DHCP Option 43 to be encoded in a specific hexadecimal TLV (Type-Length-Value) format, not plain ASCII. The correct hex string breaks down as: F1 (type/suboption for Cisco WLC), 04 (length = 4 bytes for an IPv4 address), and AC10.3205 (172.16.50.5 converted to hex: 172=AC, 16=10, 50=32, 5=05). Option B is wrong because CA10.3205 translates to 202.16.50.5, not 172.16.50.5 - it's simply an incorrect hex conversion of the WLC IP address. Options C and D are wrong because DNS-based WLC discovery requires the WLC to be registered under the hostname "CISCO-CAPWAP-CONTROLLER" in DNS, and neither the WLC's management IP nor the default gateway IP is a DNS server in this scenario.
Memory Tip: To convert an IP to hex for Option 43, convert each octet individually (e.g., 172 → AC, 16 → 10, 50 → 32, 5 → 05), and always prefix with F1 (Cisco's vendor-specific suboption) and 04 (IPv4 length). Think "F1-04-[IP in Hex]" as your formula.
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