How to use DHCP server Option 43 to discovery WLC

The Cisco IOS DHCP Server feature is a full DHCP server implementation that assigns and manages IP addresses from specified address pools within the router to DHCP clients. The following figure shows the basic steps that occur when a DHCP client requests an IP address from a DHCP server.



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 Option 43:  Option 43 is used to provide IP addresses to LAP and is required if the WLCが is in a different subnet than the DCHP server itself
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The example of option 43 on Cat6K

ip dhcp pool vlan368
   network 172.33.68.0 255.255.255.0
   default-router 172.33.68.254
   option 43 hex f104.ac21.430a

When DHCP servers are programmed to offer WLAN Controller IP addresses as Option 43 for other Cisco Aironet LAPs, the sub-option TLV block is defined in this way:

• Type—0xf1 (decimal 241)
  
• Length—Number of controller IP addresses * 4
  
• Value—List of the WLC management interfaces, typically translated to hexadecimal values
  

As you can see from the example TLV: f104.ac21.430 (ac21.430a is IP address of WLC management interface)

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