DHCP Option 43

When an AP boots it needs an IP address.

 

Then it runs the well-known hunting algorithm to discover a candidate WLC.

DHCP option  is part of hunting algorithm where it use DHCP option 43 to serve the WLCs IP address.

You can find below how to configure option 43 in DHCP scope.

In case of 1 WLC exist on the network the network we must add F104<IP IN HEX OF WLC1>

Example

WLC IP: 10.10.30.100  <0a0a1e64>  <---HEX of 10.10.30.100

F1040a0a1e64             <---How DHCP option 43 should be

In case of 2 WLCs exists on the network the network we must add

F108<IP IN HEX OF WLC1><IP IN HEX OF WLC2>

Example

WLC 1: 10.10.30.100  <0a0a1e64>    <---HEX of 10.10.30.100

WLC 2: 10.10.40.100  <0a0a2864>    <---HEX of 10.10.40.100

F1080a0a1e640a0a2864            <---How DHCP option 43 should be

In case of 3 WLCs exists on the network we must add 

F10C<IP IN HEX OF WLC1><IP IN HEX OF WLC2><IP IN HEX OF WLC2>

Example

WLC 1: 10.10.30.100  <0a0a1e64 >    <---HEX of 10.10.30.100

WLC 2: 10.10.40.100  <0a0a2864 >    <---HEX of 10.10.40.100

WLC 2: 10.10.50.100  <0a0a3264 >    <---HEX of 10.10.50.100

F10C0a0a1e640a0a28640a0a3264            <---How DHCP option 43 should be

Example

ip dhcp pool Access_Points

network 10.40.16.0 255.255.255.0

default-router 10.40.16.254

dns-server 208.67.222.222

option 43 hex f1040a0a1e64

*You can find online lot of IP to HEX converter.

Resources

https://www.youtube.com/watch?v=oOh_Iv1CHxQ&ab_channel=CiscoCommunity

https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/97066-dhcp-option-43-00.html#:~:text=On%20the%20DHCP%20server%20%2C%20option,IP%20address%20to%20the%20LAPs.&text=When%20DHCP%20servers%20are%20programmed,%2D%200x66%20(decimal%20102).

https://www.cisco.com/c/en/us/td/docs/wireless/access_point/1550/installation/guide/1550hig/1550_axf.pdf