This article provides information on how to configure the DHCP option 43 on the EX\SRX platform.
Problem or Goal:
The DHCP Option 43 feature helps the Access Point (AP) to associate with the WLC (Wireless controller) in a L3 environment (AP in one network and WLC in one network).
The Access Point boots up, performs POST, and then sends a DHCP request.
The switch should send out a DHCP offer; an IP address to use, a default gateway to use, and also the 43 TLV option. The TLV should contain the IP address of the WLC, with which the AP needs to be associated.
The following command has to be issued to configure DHCP Option 43 on EX-series switches or SRX-Firewall:
Switch@juniper#set system services dhcp option 43 byte-stream "105 112 58 49 48 46 50 53 52 46 50 51 55 46 49" ("105 112 58 49 48 46 50 53 52 46 50 51 55 46 49" is same as "ip:10.254.237.1" in ASCII code)
Sample configuration to add option 43 for Cisco LWAP:
The following command is issued to configure option 43 on an EX switch, when the Access Point is a Cisco device:
Switch@juniper#set system services dhcp option 43 byte-stream “hexadecimal string”
The hexadecimal string is assembled as a sequence of TLV values for the Option 43 sub option: Type + Length + Value. The Type is always (for Cisco aironet series) the 0xf1suboption code. The Length is the number of controller management IP addresses multiplied by 4 in Hex. The Value is the IP address of the controller that is sequentially listed in Hex.
A controller for the network is present with the 10.254.237.1 management interface IP address.
The type is 0xf1.
The length is 1 * 4 = 4 = 0x04.
The IP addresses translate to 0xac 0x10 0x15 0x8c.
When the string is assembled, it yields f104ac10158c.