Question 57 of 240 from exam 400-351: CCIE Wireless Written Exam

# Question 57 of 240 from exam 400-351: CCIE Wireless Written Exam

### Question

You have 2 WLCs with management IP addresses of 192.168.11.5 and 192.168.11.6 respectively.

Your APs reside on a different subnet.

Which of the below DHCP options needs to be configured?

### Explanations

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A. B. C. D.

B.

In this scenario, the WLCs and the APs are on different subnets. When an AP boots up, it needs to discover the WLCs in the network to join one of them. One of the methods to discover WLCs is through DHCP option 43.

Option 43 provides the WLC management IP addresses to the APs during the DHCP process. The value of option 43 is a hexadecimal string that contains information such as the WLC IP addresses, vendor-specific information, and other data.

• First byte (2 hex digits): This is the option code (decimal 43).

• Second byte (2 hex digits): This indicates the length of the remaining string (in bytes) for the option, which should be equal to the number of WLC management IP addresses specified in the option.

• Remaining bytes (variable): This contains the WLC management IP addresses in a specific format.

In this scenario, there are two WLCs with management IP addresses of 192.168.11.5 and 192.168.11.6. To configure DHCP option 43, we need to use the following format for the remaining bytes:

• First byte (2 hex digits): This is the WLC type. For Cisco WLCs, it is 0xf1.

• Second byte (2 hex digits): This is the length of the IP address information for each WLC. Since the IP addresses are 4 bytes each, the length is 0x08.

• Remaining bytes (variable): This is the actual IP address information for each WLC. The format is <WLC IP address><WLC IP address>, where each IP address is 4 bytes.

So, for this scenario, we can calculate the DHCP option 43 value as follows:

• Option code: 0x2B (43 in hexadecimal)
• Length: 0x10 (16 in hexadecimal)
• WLC type: 0xF1