Option 43

Kamran Mustafayev · ‎04-11-2012

Hello,

Here is part of router configuration of dhcp for Wireless AP.

Ip dhcp excluded-address 172.16.100.1 172.16.100.100

ip dhcp pool lwapp-ap

network 172.16.100.0 255.255.255.0

default router 172.16.100.1

option 43 ascii "172.16.1.10"

ip dhcp pool client-20

network 172.16.20.0 255.255.255.0

default-router 192.168.16.1

ip dhcp pool client-21

network 172.16.21.0 255.255.255.0

I have a question is it right to use option 43 ascii? i ask because when i replace ap with my laptop it takes 172.16.100.102 ip address, i know ap use Lwapp/capwap but it doesnt see 172.16.1.10 what can you advice

thank you

blakekrone · ‎04-11-2012

You must use Option 43 HEX as shown below:

Add the Option 43 line with this syntax:

option 43 hex

The hexadecimal string in step 3 is assembled as a sequence of the TLV values for the Option 43 suboption: Type + Length + Value. Type is always the suboption code 0xf1. Length is the number of controller management IP addresses times 4 in hex. Value is the IP address of the controller listed sequentially in hex.

For example, suppose there are two controllers with management interface IP addresses, 192.168.10.5 and 192.168.10.20. The type is 0xf1. The length is 2 * 4 = 8 = 0x08. The IP addresses translate to c0a80a05 (192.168.10.5) and c0a80a14 (192.168.10.20). When the string is assembled, it yields f108c0a80a05c0a80a14. The Cisco IOS command that is added to the DHCP scope is:

option 43 hex f108c0a80a05c0a80a14

http://www.cisco.com/en/US/tech/tk722/tk809/technologies_configuration_example09186a00808714fe.shtml#p3