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john smith

IOS based DHCP option 43

hello friends,

if i have a dhcp pool configure in core switch (IOS), than to configure option 43 for wireless for the APs in the same pool, how can we configure a controller's ip address

my question is

what is the best formula or tool to convert a wireless lan controller's ip to hexadecimal for its use with dhcp pool in ios switch?


Scott Fella
Hall of Fame Guru

There are many online binary to he converter. I just use MissingCalc on my iPhone:)


Scott Fella

Sent from my iPhone

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Cisco Employee

If the AP model is not 1000 series , we use TLV format to define the option 43 :

Type is f1

Lenght : no of controller * 4

Value : ip address of each cotnroller concatenated with each others . Make sure that every octet in the ip address is represented by two hexadecimal digits.


we have two cotnrollers with management ips as follow and

so the type is f1

          length is 2* 4 = 8 ---08 in hex

ip addresses translates to

0a7e7e02 and 0a7f7f02

You can use calculator to do the conversion.

so the command to be applied is

option 43 hex f1080a7e7e020a7f7f02 

guys i was about to ask the same question i didnt get the type we have 2125 model (i have one contoller)

ip dhcp pool access-points

   network 10.X.X.0

   default-router 10.X.X.1

   option 60 ascii Cisco AP c1142 (what does this mean)

   option 43 hex f104.0a5e.dec8  what does this mean

   lease 7

why life is so hard :-) this config is taken from exsisiting i need to config the same in other site so kindly help me with option 60 and option 43 how to come up with the values

DHCP servers must be  programmed to return the option based on the access point DHCP Vendor  Class Identifier (VCI) string (DHCP Option 60). The VCI strings for  Cisco access points that can operate in lightweight mode are listed in Table F-1.

Table F-1     Lightweight Access Point VCI Strings

Access Point
Vendor Class Identifier (VCI)

Cisco Aironet 1000 series


Cisco Aironet 1100 series

Cisco AP c1100

Cisco Aironet 1130 series

Cisco AP c1130

Cisco Aironet 1200 series

Cisco AP c1200

Cisco Aironet 1240 series

Cisco AP c1240

Cisco Aironet 1250 series

Cisco AP c1250

Cisco Aironet 1300 series

Cisco AP c1300

Cisco Aironet 1500 series

Cisco AP c15001

Cisco AP.OAP15002 , Cisco AP.LAP15102, or
Cisco AP.LAP15052


Cisco Aironet 1520 series

Cisco AP c1520

Cisco Aironet 1550 series

Cisco AP c1550

option 43 : Here you put the ip address of the management interface of the WLC in TLV format


If the controller have ip address

DHCP option 43 value will be calculated as follows:


L=4* number of controllers = 4*1=4 (04)

value is the ip address of the management interface in Hex format : 0A010101

so option 43 in this case is fa040a010101


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Hi folks,

juts found this topic as I was trying to figure out how does that work.. As I couldn't find any tool to do that I put a very quick and dirty script together, which should do the job... 


ips=['', '']


for ip in ips:
for oct in ip.split('.'):

print 'option 43: %s%s%s' % (type,wlcs,iphex)

Edit the ips list with the IP/IPs of your controllers and copy->paste it to a python shell... It should work .. ;-) 

Hope this helps someone.. 

Thanks for the lovely explanation but the only thinmg which i dont understand is

option 43 hex f104.0a5e.dec8   (why the format has . normally hexa doesnt have that so do we have to use it or not

secondly if I give managment IP to AP (staticaly ) and WLC has same subnet (suppose /24) then do i have to do this excersise of hexa etc


There is no need for the . while entering the option

If you have the AP and the cotnroller on the same subnet there is no need for DHCP option 43 cause the AP shoule be

able to hunt the wireless lan controller through broadcast discovery request on its local subnet. This broadcast discovery request will be intercepted by the controller on the local subnet by sending back a discovery response to that request.

From the discovery response the AP gets more info about the controller and proceed with the rest of steps of Join process.


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You can add the TLV without any intervening delimiters such as “.”

You have to use TLV with option 43 hex

Well if the AP is in the same subnet as the WLC there is no need to configure DHCP option 43 cause the AP

will be able to discover the controller through broadcast discovery request on its local subnet which will be

intercepted by the controller on the same subnet and reply accordingly.